British Association for the Advancement of Science

EDITED BY PROFESSOR CHAS. LAPWORTH, LL.D., F.G.S.

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PHYSIOGRAPHY.

The town of Birmingham lies almost in the exact geographical centre of England and Wales, midway between sea and sea. Its distance in a straight line from the three nearest sea-ports on the opposite sides of the island, Liverpool, Boston, and Bristol, is about 85 miles in each case, while its distance from London and Southampton is only a few miles more.

The main watershed of Southern Britain, which commences to the northward in the Pennine Range and divides the rivers which flow eastward into the German Ocean from those which drain westward into the Irish Sea and the Bristol Channel, enters upon the Birmingham District from the northward by way of Cannock Chase, crosses the “Black Country” about six miles to the west of Birmingham, and passes out of the district to the southward through the Lickey Hills, round the headwaters of the Avon to the Edge Hills and the Cotswolds.

The town of Birmingham and its immediate neighbourhood, is drained by the brooklets which unite to form the river Tame, the first of the southern tributaries of the Trent. Thus, physiographically speaking, Birmingham lies well within the basin of the Humber. To the west of the watershed of Dudley and the Lickey, the rivers of the district have a short and rapid descent to the main stream of the Severn; to the south eastward, they glide gently across the Midland Plain to its tributary—the soft-flowing Avon.

The physical centre of the district is the locality of Barnt Green, a point on the Midland Railway, about eight miles to the south of the town. From this point radiate the several low hill ranges which give to the neighbourhood of Birmingham its distinctive character. The first of these ranges (forming the main watershed, and constituting the natural backbone of the area) is composed of the Lower Lickey Hills and their northerly extensions—the rolling heights of Halesowen, the conspicuous mound of Rowley Regis (820 feet), and the beautifully wooded heights of Dudley Castle (730 feet), the Wren’s Nest, and Sedgley Hill. To the west of this axial ridge, a second range bearing points of a somewhat greater elevation, stretches from the same locality of Barnt Green through the Upper or Bromsgrove Lickey Hills (900 feet) to Hagley, where it is known as the Clent Hills (1,028 feet). These look out far and wide over the beautifully fertile valley of the Severn, and are continued to the north-westward in the heights of Stourbridge and Abbots Castle. To the east of the main Lickey and Dudley axis, the country is less conspicuously diversified. The hill-ranges are broader, and rise almost imperceptibly from the surrounding plains. The most important of these less elevated areas forms what may be termed the Birmingham plateau. This is an irregular strip of broken ground, about twenty miles in length by four or five miles in breadth, which takes origin from the north-eastern slopes of the Lickeys between Northfield and Halesowen, and sweeps northwards through Harborne, Birmingham, Barr and Sutton Park, into the wild district of Cannock Chase. On this irregular plateau stand the town of Birmingham and its suburban villages of Harborne, Edgbaston, Moseley, Aston, Handsworth, and Sutton Coldfield. The western side of the plateau overlooks the “Black Country.” It is marked out by the terrace of Smethwick, Sandwell, and Great Barr, and culminates in the conspicuous fir-topped hill of Barr Beacon (800 feet). The eastward margin of the plateau is much less pronounced, and subsides gently into the great Midland plain of Warwick and Tamworth, along a line drawn from Northfield, through King’s Heath, Moseley, Camp Hill, and Sutton Coldfield.

The ground forming the Birmingham plateau rises and falls into an endless succession of heights and hollows; here sinking down into broad tree-sheltered, stream-cut valleys, there rising into long low mounds and hills. The subsoil throughout is mainly gravel or sandy clay, and the underground drainage is, as a rule, excellent. The north-western half of the plateau still retains its original forest character, and the primeval aspect of the district is recalled by the wild area of Sutton Park—a picturesque admixture of long, dry, pebbly mounds, covered with thick woods of oak, ash and holly, and divided from each other by open glades of gorse patches, with long, flat, treeless expanses, shrouded in dark heather and picked out here and there with deep, clear water-pools. The central half of the plateau is now covered by the great town of Birmingham and its immediate dependencies. The town stands upon a series of broad rounded knolls, divided from each other by intervening open valleys. The more elevated points are marked by the church of St. Philip’s, Newhall Hill, Soho Hill, and the Monument; while the great maze of streets, manufactories and commercial buildings fill up all the space between. Strictly speaking, the town proper lies in the angle included between the river Tame and its little tributary the Rea. The Tame runs in a broad valley round the north-eastern side of the town to the low-lying district of Saltley, and thence takes its course north-eastward across the Midland plain towards the Trent at Burton. The little river Rea, which is the Birmingham river par excellence, runs from the Lickey Hills through the south-eastern corner of the town, across the low-lying district of Digbeth, and joins the Tame at Saltley.

The south-western portion of the Birmingham plateau is occupied by the fashionable district of Edgbaston and the neighbouring suburbs of Harborne and Moseley. While the original upland character of the plateau is still distinctly apparent, the dwellers in this southern area have in all other respects utterly changed its former aspect. The land has been reclaimed and enclosed. In place of the wild oak and ash, we have masses of the Elizabethan elm, the fir and the beech; and in place of the wild heather, cultivated lawns and grassy fields. Every advantage has been taken of the natural resources of site and soil; and the result is that Edgbaston and its surroundings form one broad expanse of mansions, woods and fields, well worthy of the town and neighbourhood.

To the westward of the Birmingham plateau lies the district of the “Black Country,” of which the town of Dudley is the natural centre. Compared with the Birmingham plateau, it is a lowland district of wild confusion—a maze of mines, chimneys, factories, and straggling villages and towns, shrouded in a canopy of smoke and steam. The natural soil is generally hidden from sight by heaps of mining spoil, and mounds of rubbish, cut through in all directions by lines of railway and broad canals. The beautiful wooded hill of Dudley, crowned with its grey keep, and the neighbouring oak-clad ridges of the Wren’s Nest and Sedgley, rise like islands of verdure out of the dark sea of mining ground around, and look strangely out of place amid their gloomy surroundings.

To the east of the Birmingham plateau lies the broad plain of Tamworth and Nuneaton, watered by the sluggish stream of the Tame. The plain is continued far to the southward through the richly wooded district of Warwick, Alcester, and the old Forest of Arden, and thence down the valley of Shakespeare’s Avon, to the terrace of the Edge Hills and the northern slopes of the Cotswolds.

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GEOLOGY. (BIRMINGHAM DISTRICT).

Paleozoic Rocks.

BY PROF. C. LAPWORTH, LL.D., F.G.S.

Introduction.

The Birmingham district, or that area of which Birmingham constitutes the natural capital and commercial centre, extends from Stafford on the north to Tewkesbury on the south, and from Wellington on the west to Leicester on the east, forming an area about 60 miles in length by 50 in breadth.

In no single district in Britain is the relation of the physiography of the country seen to be more strikingly dependent upon its geological structure than within the limits of the Birmingham district. Every hill, ridge, plain, and valley of any importance is a mere reflex of the underground geology. The local distribution and physical peculiarities of its rock formations afford a natural and complete explanation of all its special scenic peculiarities.

The dominant geological formation of this Midland area is the great Mesozoic formation of the Triassic or New Red Sandstone, which stretches through Southern Britain in a continuous band from Hartlepool to Exeter, and divides the broken and contorted Paleozoic rocks of the west from the flat-lying Neozoics of the east. This great band of New Red Sandstone attains its widest extension in the north of the Birmingham district, between Eccleshall and Charnwood Forest, where its transverse diameter is about 50 miles. Within the limits of the Birmingham district, however, its diameter rapidly decreases, until in the extreme south, in the neighbourhood of Worcester and the Malverns, its breadth is reduced to about 10 miles.

The red rocks of this Triassic formation not only form by far the most predominant and most conspicuous geological feature of the district at the present time, but not long since, geologically speaking, they must have extended over the entire area in one unbroken expanse. They now constitute a sheet of red sandstones and marls, through which protrude, in numerous bands and patches, the older Paleozoic rocks. Although nowhere very steeply inclined, these red beds of the Triassic have been bent into several long low arches, or broad domes, whose longer axes range approximately north and south. The summits of many of these arches have been denuded, and the underlying older rocks have again been bared to-day. Four of these arches are especially conspicuous, those of the Wrekin, Malvern, Dudley, and Nuneaton. In each of these the underlying Coal Measures are laid bare, forming the four coalfields of Coalbrookdale, Forest of Wyre, South Stafford, and Eastern Warwick, all of which shew round their outer margins a narrow band of the intermediate formation of the Permian. In each of these anticlinals, too, the denudation of the core of the arch has been sufficient to wear away the Carboniferous from its centre, and to expose to view yet older formations—the Old Red Sandstone in the Forest of Wyre, the Silurian in South Staffordshire, the Malverns, and Coalbrookdale, and even the Upper Cambrian and its underlying igneous rocks in the Wrekin, the Lickey, and near Nuneaton. With the exception of the Silurian of Abberley and Dudley, and the recently discovered Cambrian of Nuneaton, however, these pre-Carboniferous rocks are comparatively inconspicuous, rising up merely in narrow bands in the cores of long wedge-shaped hills.

From the economical as well as from the structural point of view, by far the most important of these geological arches is that of South Staffordshire, which is the southward continuation of the Pennine chain, and part of the true backbone of Southern Britain. The central axis of this arch runs, as we have seen, through the Dudley Hills, and dies away in the complex of faults to the south of the Lickeys. On the natural consequences of the rise of this arch, all the physical, scenic, and economic peculiarities of the central parts of the district are essentially dependent. The hills and plains around Birmingham are all more or less related to this grand anticlinal—the hills marking the uplifted edges of the harder rocks, the limestones, sandstones, and pebble beds; and the plains, the position of the gently inclined soft shales and marls. It has brought within workable distance of the surface the coals and ironstones of South Staffordshire, and the valuable limestones of the Dudley Hills, and it has had its final effect in bringing together the overflowing population of the town and district.

The original simplicity of the geological structure of the floor of the Birmingham District is much complicated by fractures, faults, and unconformities. The Wrekin and the Malverns are both affected by profound dislocations. The South Staffordshire Coldfield is bounded both on the eastward and the westward by faults of more than ordinary magnitude, while a long straight fault more than 20 miles in length runs through the south-eastern part of Birmingham itself, and flings down the Keuper marls of the Warwick plain against the older sandstones of the Birmingham plateau.

In the Birmingham District as everywhere in Britain, the Triassic formation rests unconformably upon everything below. At the same time, its members overlap each other more or less irregularly, and shew a rapid diminution in thickness when followed from west to east. Thus it happens that not only do the pre-Triassic rocks make their appearance in their expected positions along the main anticlinal lines, but many of the old ridges of PalÆozoic rocks, which rose out of the Triassic waters, have had their enveloping pall of red sandstone removed from their flanks and summits, which have thus been bared once more to the light of day. Such are, in part, the ridges of the Wrekin, the Malverns, the Lickeys, and the Forest of Charnwood.

In the valley of the Severn, to the west of Birmingham, the strata run in narrow bands. The central portion of this valley lying between Coalbrookdale and Bridgnorth, to the west of the main anticlinal of the Birmingham district, owes all its striking beauty and variety to the rapid alternations of hard and soft strata which occur within its limits.

In the great Midland plain to the east of Birmingham, the strata are spread out in broad sheets. The plain is underlain in great part by the comparatively homogeneous flat lying Keuper marls, with their intercalated bands of harder sandstones. Its scenery is consequently less varied than that of the Severn valley, but it is rich in that sweet sylvan beauty which is almost peculiar to the English landscape, and it forms one broad expanse of gently rolling farmland and woodland, whose green crested waves sweep onward to the east and south, mile beyond mile, till they break against the long shore-like scarp of the harder Jurassics.

The Local Rock Formations.

As will be apparent upon a study of the accompanying geological map, the geological formations exposed within thirty miles of Birmingham, include the entire stratigraphical succession between the Cambrian and the middle portion of the Jurassic, with two notable exceptions. The two formations locally wanting are the Ordovician and the Old Red Sandstone. The nearest known Ordovician rocks occur in central Shropshire, to the east of Church Stretton; the nearest Old Red Sandstone beds are met with to the south of the Forest of Wyre. The natural sequence of formations, and the localities where the several formations are most conspicuously displayed, are given in the following table:—

Table of the Geological Formations of the Birmingham District.

MESOZOIC, OR SECONDARY ROCKS.
Liassic.	Middle Lias (Marlstone)—Edge Hill, Fenny Compton.
	Lower Lias Clays—Harbury, Rugby.
Rhoetic.	Marls and White Lias—Harbury, Knowle, Wooten Wawen.
Triassic.	Upper Trias or Keuper:
	(a) New Red Marl—Moseley, King’s Norton, &c., &c.
	(b) Lower Keuper or Waterstones—Birmingham, Warwick.
	Lower Trias or Bunter:
	(a) Upper Mottled Sandstone—Harborne, Edgbaston, Hockley.
	(b) Pebble Beds and Conglomerate—Sutton Park, Smethwick.
	(c) Lower Mottled Sandstone—Clent Hills, Stourbridge.
PALÆOZOIC, OR PRIMARY ROCKS.
Permian, or Dyassic.	(a) Permian Breccia—Clent Hills, Northfield.
	(b) Red Sandstones and Marls—Halesowen, Enville, Rubery.
Carboniferous.	(a) Upper Coal Measures with Spirarks Limestone, &c.—Sandwell, Arley.
	(b) Lower Coal Measures—Oldbury, Bilston, Hawkesbury.
	(c) Millstone Grit—Absent near Birmingham, present near Colebrookdale.
	(d) Carboniferous Limestone—Absent.
Old Red Sandstone or Devonian	Absent near Birmingham, present in Forest of Wyre.
Silurian.	(a) Ludlow Shales and Limestones—Sedgley Hill.
	(b) Wenlock Shales and Limestone—Dudley Hill, Wren’s Nest, Walsall.
	(c) Woolhope Beds—Barr and Rubery.
	(d) Llandovery or Mayhill—Rubery.
Ordovician.	Absent.
Cambrian.	Upper Cambrian:
	(a) Tremadoc Beds and Lingula Flags.—Shineton, Nuneaton, Lower Lickey, and Malverns.
FUNDAMENTAL, CRYSTALLINE AND IGNEOUS ROCKS.
(a) Charnwood Volcanic Rocks—Charnwood Forest, Caldecote Hill, The Wrekin.
(b) Malvern Crystalline Rocks—North Hill, Hereford Beacon, &c.

The Fundamental Crystalline and Volcanic Rocks of the Malverns, the Wrekin, And Charnwood Forest.

The rocks which undoubtedly occupy the lowest place in the geological formations of the Birmingham district are those crystalline and partly schistose masses which form the core of the Malvern Hills; and certain well-marked volcanic rocks which occur at the Wrekin and Nuneaton, and which appear to have their equivalents in the great igneous series of Charnwood Forest. That all these more or less crystalline rocks are of higher antiquity than the Upper Cambrian of Wales is demonstrated by the fact that fossiliferous rocks containing Cambrian fossils of this age overlie them, while the lowest recognisable zones of these overlying fossiliferous rocks (the Hollybush sandstone of the Malverns, the quartzite of the Wrekin, and the Hartshill quartzite of the neighbourhood of Nuneaton) are in part composed of their fragments. Whether, however, they belong in part to the Middle or Lower Cambrian, or wholly appertain to the earlier formations of the Archean, must as yet remain an open question.

(a.) Malvern Hills.—The core of the Malvern Hills is composed of a coarse syenitic, and more or less gneissose rock, pierced by veins of quartzo-felspathic rock of igneous origin (Hereford Beacon, &c). The main mass which is coarsely crystalline, becomes occasionally distinctly gneissose and even schistose, and its mineral bands strike from north-west to south-east, i.e., transverse to the general trend of the Malvern Ridge. The basement beds of the Hollybush sandstones (Cambrian) and the Llandovery rest unconformably upon this rock, which has consequently been claimed by some geologists as distinctly of Archean age, representing in part the Laurentian of Logan.

The best localities for studying the essential characters of the Malvern rocks are the quarries of the North Hill and the Wych, and the eastern slopes of the hills between Malvern Wells and Herefordshire Beacon.

(b.) The Wrekin.—The core of the beautiful hill of the Wrekin is formed by a magnificent series of highly acidic volcanic rocks—rhyolitic lavas and ashes. As first pointed out by Dr. Callaway, they rise out unconformably from below fossiliferous rocks of Upper Cambrian age. (Hollybush Sandstone and Shineton Shales) and are believed by him to be of Archean age. The finest exhibitions of the volcanic ashes of the group are met with in quarries on the flanks of the Wrekin itself, while the rhyolitic lavas occur in scattered localities along the hill. A broad mound of the same igneous series rises out from below the Triassic to the south of Walcot Station, and a most beautiful and instructive section of banded and spherulitic rhyolites is shewn in the quarry at the locality known as the Lee Rock.

The truly volcanic nature of these remarkable rocks was first pointed out by Mr. S. Allport, F.G.S., and their original characteristics, and the changes they have undergone since their formation, have been described by him in a well-known series of memoirs. Their geological position, and their relation to the associated fossiliferous strata, and to the similar rhyolitic rocks of Caer Caradoc and Pontesbury have been fully discussed by Dr. C. Callaway, F.G.S.

(c.) Nuneaton (Caldecote Hill).—A thin group of volcanic breccias and tuffs, with associated quartz-felsites, and diabase, rises out from below the Upper Cambrians of Nuneaton, in the Park of Caldecote Hill. The lowest zone of the overlying Cambrian Hartshill quartzite is in part composed of their fragments. The ashes are shewn in old cuttings to the north-west of Caldecote Lodge, the quartz-porphyries and diabase in an old quarry about a quarter of a mile to the southward, while the breccia composed of the fragments of these old rocks, in the base of the Cambrian quartzite is best shewn on the tramway still farther to the southward, leading down to the Coventry Canal.

(d.) Charnwood Forest.—This district is formed of an island of ancient igneous and stratified rocks rising out from below the Upper Trias. The stratified rocks are almost wholly composed of materials of volcanic origin, and shade off on the one hand into coarse volcanic agglomerates, and on the other into fine green slates like those of the Borrowdale series in the Lake District, to which indeed the whole of the bedded Charnwood rocks bear a striking resemblance.

The stratified volcanic rocks are pierced by numerous igneous intrusions. The most conspicuous are those classed by Professor Bonney, F.R.S., as syenite. These are most conspicuous near Groby, Bradgate, and generally in the south eastern parts of the Charnwood area. A mass of beautiful hornblendic granite rises through the Trias immediately to the east of Charnwood Forest at Mount Sorrel, near Barrow on Soar. A few later dykes of altered andesite occur within the forest itself, and diorite in the outlier of Brazil Wood.

To the south of Charnwood Forest, several remarkable points of syenitic rock protrude through the flat-lying Trias. The most conspicuous of these are the hills of Sapcote, Croft, and Enderby.

There is no direct evidence of the Cambrian or pre-Cambrian age of the Charnwood rocks, but strata identical with the fossiliferous Stockingford shales (Upper Cambrian) of Nuneaton, have been pierced in several borings through the Trias near Leicester, Market Bosworth, etc., and appear to rest at once upon the Charnwood rocks, as do the Nuneaton beds upon the Caldecote volcanic group.

Cambrian Rocks.

No fossiliferous strata unequivocally of Lower Cambrian age occur within the limits of the Birmingham District; but strata of Upper Cambrian age are met with in several localities. They were first recognised by Professor Phillips in the area of the Malvern Hills, and have been subsequently detected within the last few years at the Wrekin, at Nuneaton, and in the Lower Lickey Hills.

Malvern Hills.—The Upper Cambrian beds of the Malverns rest upon the crystalline rocks of the axis of the hills to the south of Herefordshire Beacon, along the slopes of Midsummer Hill and Keys Hill. The lowest zone is the Hollybush Sandstone, a light green micaceous rock, containing tubes of sea worms and Kutorgina cingulata.

The Hollybush Sandstone is succeeded by shivery shales, somewhat sandy below, and becoming darker and more carbonaceous above.

In their lower beds they yield:—Obolella Salteri, Obolella sagittalis, Lingula pygmea, etc. In their middle beds they afford Pellura scarabeoides, Spheropthalmus alatus, Agnostis pisiformis, Agnostus trisectus, etc., well-known fossils of the Upper Lingula Flags (Dolgelly) of North Wales.

Their highest beds contain Dictyonema sociale, a fossil which passes up into the succeeding Tremadoc Slates.

The rest of the local succession of the Cambrian rocks is hidden by the unconformable overlap of Silurian.

The Hollybush Sandstone and the overlying sandy shales contain numerous intercalated volcanic rocks, some of which are of the age of the surrounding strata, while others are intrusive.

Nuneaton District.—In the neighbourhood of the town of Nuneaton in eastern Warwickshire, a strip of Cambrian rocks, about eight miles in length by one in breadth, has been detected within the last few years. The rocks consist of volcanic ashes, quartzites and thin-bedded shales, pierced by dioritic dykes. These strata were formerly mapped as altered Millstone Grit and Carboniferous shale, and their Cambrian age has only been recently demonstrated by the discoveries of Birmingham geologists. The complete succession is as follows:—

(1.) Caldecote Volcanic Group.—Well-bedded tuffs and volcanic ashes (see ante) with masses of Quartz-felsites and diabase.

(2.) Hartshill Quartzite.—Thick-bedded quartzites, with occasional layers of sandy shale.

(3.) Stockingford Shales.—

(a.) Lower Division.—(Obolella Beds) Purple and green shales with Obolella Salteri, Lingulella pygmea, Lingulella lepis, Acrotreta, Protospongia, &c.

(b.) Upper Division.—(Agnosias Beds) Grey and black shales with Agnostus pisiformis. Beyrichia Angelini and Lingulella Nicholsoni, in the lower zones, and Spheropthalmus alatus and Dictyonema in the upper zones.

These Cambrian rocks are overlain unconformably by the Coal measures to the west, and by the Keuper beds to the east; the boundary of the area is, however, locally defined by lines of fault.

The basement beds of the Hartshill Quartzite are locally composed of fragments of the underlying volcanic rocks (Caldecote Beds). The Quartzite itself, which forms the chief road metal of the neighbourhood, is laid bare in a long series of quarries between Nuneaton and Hartshill.

The overlying purple and green shales of the Stockingford Beds range from Marston Jabet, south of Chilvers Coton to Atherstone Outwoods. The best section is seen in Parley Park Lane near Atherstone, and the fossils have been obtained from this section, from Atherstone Oakwoods, Camp Hill, and Marston Jabet.

The best section of the succeeding grey and black Shales occurs in the cutting of the Midland Railway near Stockingford, which gives its name to the formation. Their fossils have been procured from the rocks of this section; from the cutting at Chilvers Coton, the banks of the Coventry Canal, from Oldbury reservoir, Mawbornes and Merevale Park.

The numerous intrusive dykes of volcanic rock form a conspicuous feature in the geology of these Cambrian strata. They are formed of coarse-grained diorites, much quarried for road metal, kerbs, and setts. Good sections occur in the quarries near Tuttle Hill, in the railway cuttings near Stockingford and Chilvers Coton, and in quarries near Oldbury Reservoir.

A small patch of these Nuneaton Cambrians is met with on the north-western margin of the East Warwickshire coalfield, at Dost Hill, to the south of Tamworth. It consists of the usual annelide-bearing Stockingford Shales, pierced by an intrusive mass of diorite.

Lower Lickey Hills.—The core of the Lower Lickey Hills between Barnt Green and Rubery, about eight miles south of Birmingham, is formed of a mass of quartzite identical in all its main features with that of Hartshill, near Nuneaton.

At the village of Rubery, in an exposure on the roadside, it is seen to be unconformably overlain by fossiliferous Llandovery sandstone, the basement beds of which contain fragments of the underlying quartzite in abundance. At the south-western extremity of the Lower Lickey Range the quartzites contain fragments of igneous rocks, and appear to pass down into a series of felspathic grits, pierced by dioritic dykes similar to those of the Nuneaton District. Good sections of the quartzites are laid bare at Rubery Station, at the village of Rubery, and in a large quarry near the roadside, a mile northward from Kendall End. In the last-named locality the quartzites are seen greatly folded and faulted.

Wrekin District.—In the Wrekin area the great volcanic series of the hills is immediately overlain by a quartzite similar to that of the Hartshill and the Lickey, the basement bed similarly containing fragments of the underlying volcanic rocks. The quartzite is succeeded by the Hollybush sandstone, with its characteristic fossil, Kutorgina cingulata.

A broad area, lying between the Hollybush sandstone and the unconformably overlying Silurian rocks of Buildwas, is occupied by a series of Upper Cambrian rocks, denominated by Dr. Callaway the Shineton Shales, and characterised by the forms:—Olenus Salteri, SphÆropthalmus, Asaphellus Homfrayi, &c., Bryograptus Callavei, &c., allying them with the Tremadoc Beds of North Wales.

Silurian Rocks.

The rocks of the Silurian System are fully developed within the limits of the Birmingham District, under their most typical aspect. The well known localities of Dudley and Barr have been famous in the geological world since the publication of Murchison’s great work, the Silurian System; and the abundance and beauty of the fossils of the limestone rocks of the district place it next to the typical area of Central Shropshire as the representative country of the Silurian rocks.

The Silurian strata are all of the well-known Salopian type, shewing several thick-bedded limestones, occurring on distinct horizons in a great thickness of dark blue or grey nodular shales and mudstones. They make their appearance in sharp anticlinal arches in the South Staffordshire coalfield, and along its faulted margins. Four of these exposures occur along the crest of the Lickey-Dudley anticlinal—at Rubery, Dudley Castle Hill, the Wren’s Nest, and Sedgley. The largest continuous exposure is that near the town of Walsall, on the eastern margin of the coalfield.

All the Silurian formations from the Mayhill Sandstone to the Ludlow (Aymestry) Limestone are recognisable, but the terminal Downton sandstone is lost below the unconformably overlying Carboniferous. None of the localities, however, shew the complete consecutive series, which is made out by piecing together the sections occurring in the several areas.

(1.) Lower Lickey Hills.—

(a.) Landovery or Mayhill Rocks.—The usual red and grey Pentamerus sandstone of the Mayhill formation is exposed along the north-west flank of the Lower Lickey Hills. It may be seen resting unconformably upon the Cambrian quartzite in the village of Rubery, and at Leach Heath. Casts of fossils are abundant in some of the sandstones a few feet above the base of the formation, and include the well known forms:—Pentamerus oblongus, Pentamerus lens, Strophomena expansa, Attrypa reticularis, etc.—These may be collected from the rocks at the village of Rubery, and from the fragments of sandstone scattered over the fields between the Asylum and Leach Heath.

(b.) Woolhope or Barr Limestone.—The Llandovery sandstone is followed (in a stream section below the Asylum) by pale blue shales and mudstones containing a bed of hard calcareous rock, affording examples of Illenus Barriensis, Atrypa reticularis, Encrinurus punctatus, Rhynchonella Lewisii; but the section is a poor one, and is covered up almost immediately by the overlying Carboniferous.

(2.) Walsall and Barr.—This is the typical area for the well known Barr Trilobite Illenus Barriensis. The quarries of the Woolhope Limestone which afford it are now disused, but a good section of the fossiliferous shales above is displayed in the railway cutting between Aldridge and Walsall. The overlying Wenlock or Dudley Limestones are mined at the town of Walsall itself, but good fossils are now comparatively rare.

(3.) Dudley and the Wren’s Nest.—By far the most notable and interesting of the Silurian exposures are those of the neighbourhood of Dudley. In the three exposures of Dudley Castle, the Wren’s Nest, and Sedgley Hill, the Silurian limestone rises up in steep dome-like forms. This limestone, which is that of the Wenlock of Siluria, is here composed of two calcareous bands—the higher about 28 feet in thickness, and the lower about 42 feet—separated from each other by an intermediate zone of about 90 feet of gray shales. The limestone has been worked for centuries as a flux for the ironstones of the coalfield. The hills have been mined to a great depth, and all the best limestone rock extracted. The intervening and enveloping shales have been allowed to remain, and the present structure of the hills is that of a central dome surrounded by two enveloping shells, separated from each other by two more or less empty spaces. Where the dip of the rock is high, and these excavated parts are exposed, they form deep moat-like hollows, bounded by walls of shale. Where the dip is low, and the overhanging rocks are supported by the vast pillars left by the workmen, these excavations form magnificent caverns of peculiar weirdness and beauty. In the heart of the hill at greater depths they form damp gloomy chasms of enormous extent, which can only be seen to perfection when lit up by artificial light.

The Dudley limestone bands and the surrounding calcareous shales have long been famous for the abundance and beauty of their included fossils. Many of the type species of Murchison’s Silurian System came from this locality; but since the superficial limestones have been worked out, good specimens are exceedingly rare. An excellent collection of the fossils of these beds is laid out in the Dudley Museum, and another in the Geological Museum of the Mason College. Many good collections are in the possession of private individuals in Dudley and elsewhere.

The best localities for fossils at present are the shaly slopes on the flanks of the Wren’s Nest, where the usual Wenlock Brachiopods and Corals are abundant, but the beautiful Trilobites of the formation are but rarely met with.

The Wenlock limestone occurs both in the Dudley Castle Hill and in the Wren’s Nest. The Aymestry limestone is only met with in a single locality on the flanks of Sedgley Hill, where it yields occasional specimens of its characteristic fossil, the Pentamerus Knightii.

Carboniferous Rocks.

Rocks of Carboniferous age make their appearance at four distinct localities within the limits of the Birmingham District, viz., in the coal fields of Coalbrookdale, the Forest of Wyre, South Staffordshire, and East Warwickshire. The strata exposed on the last three of these coalfields are those of the upper Carboniferous or Coal measures; neither the Carboniferous limestone nor the Millstone grit being met with outside the limits of the coalfield of Coalbrookdale.

In the Forest of Wyre the Coal measures rest upon the Old Red Sandstone, in the South Staffordshire Coalfield upon the various members of the Silurian, and in the East Warwickshire upon the Upper Cambrian rocks. In these three coalfields a two-fold division of the Carboniferous is recognisable:—

(a.) The Lower Coal Measures proper, consisting of grey sandstones and shales with occasional coal seams, some of which are of remarkable thickness.

(b.) Upper Coal Measures, or Halesowen grey and red sandstones, brick clays and marls, with occasional coal-seams, none, however, of commercial value.

In the South Staffordshire and East Warwickshire coalfields, the well known “Spirorbis Limestone” of the Upper Coal Measures occurs in its normal place near the summit of the Carboniferous series.

South Staffordshire Coalfield.—The Carboniferous rocks of South Staffordshire are arranged in a broad dome about 23 miles in length by 6 in breadth. Their basement beds rest unconformably upon the Silurian around the flanks of the Dudley Hills, and in the neighbourhood of Walsall. Their highest beds dip conformably below the Permian rocks at the southern extremity of the coalfield south of Halesowen, and are overlapped unconformably by the Triassic pebble beds at its northern extremity, in the district of Cannock Chase. The eastern and western boundaries of the coalfield are formed by lines of fault, which have flung down against the Coal Measures the various members of the Permian and the Triassic. The total thickness of the Carboniferous beds is about 1,300 feet, and the normal succession in the central and highest part of the coalfield is as follows:—

Upper Coal Measures.—

2a. Halesowen Sandstone Group, 600 to 800 feet.

2b. Red Coal Measure Clays.

Lower Coal Measures, 500 to 600 feet, containing several excellent coal seams, of which the following are the most important:—

(a.) Brooch Coal, 4 feet.

(b.) Thick Coal, 30 feet.

(c.) Heathen Coal, 3 feet.

(d.) New Mine Coal, 2 to 11 feet.

(e.) Fire Clay Coal, 1 to 14 feet.

(f.) Bottom Coal, five feet and above.

These measures include several zones of workable ironstone, of which the most important are:—

(1.) The Pins and Pennyearth ironstones, below the Brooch coal.

(2.) The Whittery and Gubbin ironstones, below the Thick coal.

(3.) The Blue Flats, Silver Threads and Diamond Ironstones, below the Bottom coal.

For its size the South Staffordshire coalfield has proved itself the richest mineral area in Britain. Thick coal seams, rich bands of ironstone, and great thicknesses of Silurian limestone, all occur within a short distance of each other, and all within easy reach of the miner. The natural result has been that the South Staffordshire coalfield and its immediate neighbourhood has been the great coal and iron mart of Central Britain, and the abundance and cheapness of its material it has afforded, have rendered Birmingham and the “Black Country” the hardware workshop of the world.

Almost all the available coal seams and ironstone beds within easy reach have been long since practically worked out, but there is still much excellent coal and iron to be obtained at greater depths, especially in the northern part of the coalfield. Of late years the Triassic rocks which surround the coalfield have been pierced in order to reach the Coal measures beneath. An entirely new coalfield has been developed in this manner in the district of Cannock Chase; and two most remarkable collieries, those of Sandwell Park, and Hamstead, have been opened in the neighbourhood of Birmingham itself.

The area immediately underlain by the Coal measures constitutes the district of the “Black Country,” which extends from the western margin of Birmingham to the fringe of Cannock Chase. It includes within its limits, the large towns of Dudley, Walsall, Wolverhampton, Bilston, and others of scarcely less note.

The most remarkable seam of the South Staffordshire coalfield is that known as the Ten yard or Thick coal, a continuous bed of workable coal from 25 to 30 feet in thickness. This underlies all the south central part of the field in the area enclosed by Smethwick, Oldbury, Dudley, Walsall and Bilston. To the southward near Halesowen it thins out and becomes mixed with shaly material. It is in reality composed of 13 or 14 superimposed coal seams, which form an apparently unbroken mass, but are easily distinguished individually by the practised Thick coal miner. As we pass northward from the typical Thick coal area towards Walsall and Cannock Chase, the component seams become separated by intercalated sandstones and shales, so that eventually in the district of Essington and Pelsall the Thick coal is represented by 14 distinct coals occurring at intervals in a mass of sandy rock, between 500 and 600 feet in total thickness. The Thick coal is known to extend far to the eastward, beyond the present margin of the South Staffordshire coalfield. The first attempt to reach it through the red ground (Permian) was made under the bold and skilful guidance of the late Mr. Henry Johnson, C.E., of Dudley, at the locality of Sandwell Park. The coal was reached in 1873 at a depth of 1,250 feet and found to be of its original thickness, and of excellent quality. The next attempt which was made at Hamstead Hall, about three miles outside the limit of the coalfield, was even bolder and more hazardous, but it was eventually crowned with equal success; the Thick coal being reached at a depth of 1,800 feet. As the demand for coal increases, other collieries will doubtless be started at fresh localities outside the limits of the coalfield, for there can be no question that the Thick coal extends far to the eastward, under and beyond the town of Birmingham itself.

The strata of the South Staffordshire Coalfield afford the usual fossils of the British Coal Measures. The roofs of the coal seams, and the layers of carbonaceous shale, locally furnish well preserved examples of Lepidodendron, Sigillaria, Calamites, Annularia, Pecopteris, Neuropteris, etc., often associated with abundant specimens of the peculiar Unio-like shell, Anthracosia: while the ironstone nodules occasionally yield fragmentary Crustaceans and Insects. Marine fossils are principally confined to the lower beds of the series, below the Thick coal. Owing to the absence of true limestone beds in the coalfield, the characteristic corals, &c., of the Carboniferous are absent, but the following marine forms are not uncommon in the lower ironstones:—

Lingula elliptica, Discina nitida, Producta scrabicula, Conularia quadrisulcata, Aviculopecten scalaris, Gyracanthus farmosus, Megalichthys Hibberti, Poecilodus angustus.

These have been met with at several localities near Walsall, Oldbury, Old Hill, Kingswinford, and Oldswinford, etc.

The rocks of the South Staffordshire coalfield are pierced locally by sheets of igneous rock. The most important of these is a mass of dolerite about two miles and a half in length, which caps the long ridge of Rowley Regis. It is traversed by several mining shafts, which pass through the dolerite into the workable coals below. Other igneous masses occur near Dudley, and at Pouk Hill, near Walsall.

The East Warwickshire Coalfield.—The rocks of this coalfield form a narrow strip about 15 miles in length, ranging from Tamworth on the north to Bedworth on the South. The coalbearing strata rest unconformably upon the Cambrian below, and pass up conformably into the Permian above. The sequence of the beds is practically identical with that of South Staffordshire—the richer coal measures being all confined to the lower part of the Carboniferous series, and passing up through a group of coloured clays into a final group of barren sandstones. In the north of the coalfield five workable seams of coal occur, separated by many feet of barren measures. As they pass to the southward the intermediate strata thin out, and the coal-beds practically come together at Hawkesbury to form one Main coal seam, as do the corresponding members of the Thick coal of South Staffordshire. It is probable that the two coalfields were formed in the same general area of deposition, and except for the possibility of its destruction by erosion prior to the deposition of the Triassic, it might be suggested with safety that the Thick coal of South Staffordshire extends in a continuous sheet under the red rocks of Northern Warwickshire from Smethwick to Hawkesbury.

Forest of Wyre.—Unlike the strata of the other coalfields, the Carboniferous rocks of the coalfield of the Forest of Wyre are comparatively barren of good coal seams. The best, which is locally known as the Main coal, is about seven-and a-half feet in thickness, and occurs at an average depth of 300 feet.

Coalbrookdale.—This coalfield, which lies to the east of the Wrekin, covers an area of about 28 square miles. It originally contained about 28 coal seams, but the majority of these are now practically worked out. The succession includes the Carboniferous limestone, the Millstone grit, and the Lower coal-measures in conformable sequence. The Upper coal-measures rest in a hollow eroded out of the Lower coal-measures beneath, forming what is locally known as the “Symon Fault.”

Permian or Dyassic.

The Permian rocks of the Birmingham District are totally distinct in their petrological characters from those of the typical area of Yorkshire and Durham. No true limestones are present, and the formation is wholly made up of red sandstones, marls and beds of angular breccia.

The lowest zones of the Permian repose conformably upon the Upper Coal Measures of the South Staffordshire Coalfield in the slopes of the hills to the south of Halesowen, and its strata are seen in corresponding relation to the Carboniferous on the east of the Coalfields of the Forest of Wyre and Coalbrookdale, and to the west of the Coalfield of Eastern Warwickshire.

The Permian is everywhere covered up unconformably, or locally overlapped, by the various members of the Triassic formation; all the subdivisions of the Triassic series being found resting immediately upon it in turns as they are followed from the valley of the Severn to the neighbourhood of Charnwood Forest.

In the neighbourhood of Enville and the Forest of Wyre, three divisions are recognisable in the Permian, viz.:—

(1.) Lower Red Sandstones and Marls, with bands of calcareous conglomerate.

(2.) Coarse Breccia.

(3.) Upper Red Sandstones and Marls.

Round the South Staffordshire Coalfield the Breccia is the highest division exposed, and this only occurs in force to the south of the coalfield.

Between Tamworth and Kenilworth, to the east of Birmingham, the Permian strata floor a wide tract of country, and lie almost horizontal. Red sandstones, marls and beds of breccia occur in association, but the divisions named above are not individually recognisable.

By far the most striking local member of the Permian formation is the so-called Volcanic or Permian Breccia. It is found in scattered patches over an area of about 500 square miles, extending from the Malverns to Enville, Stourbridge, and the Lickey Hills. It is made up of angular fragments of volcanic rocks, tuffs, altered shales, grits, and slabs of fossiliferous sandstone and limestones, all embedded in paste of bright red marl or pebbly sandstone. It is usually both underlain and overlain by red sandstones and marls, but sometimes, as at Stagbury and Woodbury Hills, &c., in the Valley of the Severn, it reposes at once upon pre-Permian rock.

This peculiar Breccia is well displayed in the Clent Hills, between Hagley and Halesowen. It there reposes upon the Lower Permian Sandstones with calcareous grit bands—(which may be seen above the little Church of St. Kenelm)—and forms all the highest points of the Clent Hills, passing unconformably to the southward under the pebble beds of the New Red Sandstone. In this locality the angular fragments composing the Breccia are mainly volcanic:—rhyolites, porphyrites, ashes, and volcanic grits, embedded in a coarse matrix formed of similar materials. Other sections are seen in the Bromsgrove Lickey Hills, and in the neighbourhood of Northfield. In the last-named locality an excellent section is exposed in a lane leading from the Bell Inn to Bangham Pit. In this exposure the breccia, which shows the usual preponderance of volcanic materials, contains in addition fragments of Silurian limestone (crowded with characteristic fossils), and pieces of Landovery grit and shale.

According to Sir Andrew Ramsay,[60] this Permian breccia is probably of glacial origin, its materials having been brought down by ice in Permian times from the neighbourhood of the Longmynd in central Shropshire, where all the formations represented in its derived rock fragments occur at present in natural juxtaposition. According to Professor Jukes,[61] the fragments of the Northfield breccia, at any rate, “may have been derived from adjacent rocks, now concealed under the Permian and New Red Sandstone.”

The Triassic Rocks.

BY W. JEROME HARRISON, F.G.S.

A considerable portion of the Midland Counties of England is composed of red sandstones and marls. The town of Birmingham stands upon, and is surrounded by rocks of this character. They form the Triassic System of geologists, the first of the four grand members of the Mesozoic series.

Strictly speaking, the title Trias is a misnomer as applied to the English development of the rocks of this system. The central member of the typical German succession, the Muschelkalk, is wanting in Britain; and only the upper and lower divisions, the so-called Keuper and Bunter, are represented. The Bunter or lower Trias, consists in the Midland areas of a mass of pebble beds or conglomerate, usually underlain and overlain by variegated sandstones. The Keuper is formed of a great thickness of red marly strata, with a thick sandstone (Waterstones) at the base.

The following table shews the subdivisions of the Trias which have been recognised in England, together with (a) their maximum thickness, and (b) their thickness in the neighbourhood of Birmingham.

Classification of the Triassic Strata—

The Trias enters England on the south coast, between Torbay and Exmouth. At the little watering-place of Budleigh Salterton there is a bed of quartzite pebbles in the Trias 100 feet thick which is worthy of study in connection with the great numbers of similar pebbles that occur in the same strata round Birmingham. In West Somerset and Devon, the Triassic strata are 3,500 feet in thickness. Their subdivisions cannot be correlated with those of the Midlands, for they appear to have been deposited in a separate basin, of which the Mendips, &c., still mark the northern boundary.

Crossing into Gloucestershire, we find the vale of the Severn composed of Triassic marls, and thence northwards the “red rocks” broaden till they form the plains of Cheshire and South Lancashire on the west, and extend eastward to Warwick, Leicester, and Derby. From this great central plain of our island a long strip of Triassic sandstones and marls runs northwards, forming the Vale of Trent and the Vale of York, until finally it reaches the coast between Redcar and Hartlepool. Along the main line of outcrop—from the Malvern Hills to the mouth of the Tees—the Triassic strata incline gently, or dip, to the south-east, at from two to five degrees.

Of the two great divisions of the Trias, the lower (Bunter) is mainly sandy; while the upper (Keuper) is chiefly a stiff marl or clay. One result of this is that while the outcrop of the former is usually barren, forming much heath or waste land, as Sherwood Forest, the Keuper marls produce a rich soil, well fitted for the plough.

Owing to the soft nature of the strata, valleys are usually hollowed out in the Lower and Upper Mottled Sandstones, while the Keuper marls form an undulating plain. On the other hand the harder nature of the Bunter pebble bed, and the Lower Keuper Sandstone, causes these two rocks to form escarpments or lines of hills, parallel to each other; the abrupt face generally looking west or north-west, while the gentle slope is to the east or south-east, agreeing with the average dip.

The Lower Red and Mottled Sandstone.—Round Bridgenorth this division rests unconformably on Permian strata, and is about 650 feet thick. It is a homogeneous sandstone, of reddish-brown, yellow, and bright red colours, entirely devoid of pebbles. As we follow this stratum to the east it decreases in thickness, being only 200 feet near Stourbridge. East of the South Staffordshire field, the Lower Mottled Sandstone is entirely absent, and the Bunter pebble beds repose directly upon the Permian rocks. Geologists desirous of examining the “Lower Mottled” should visit Kinver Edge, west of Stourbridge, where this rock is well seen underlying the Bunter conglomerate. Its upper portion has here been hardened by calcareous matter, and projects beyond the pebble beds above. Caves, or “rock-houses,” have been excavated in the Edge, and in a detached mass of sandstone called the Holy Austen Rock. The Lower Mottled Sandstone is again visible on Whittington Common, between Kinver and Stourbridge. It is everywhere quite unfossiliferous. “False bedding” is especially characteristic of this division, but it is common in all the Midland Triassic sandstones.

The Bunter Conglomerate or Pebble-bed occupies the surface of the Birmingham area, along a line running from south-west to north-east. It extends from Worcester, by Bridgnorth, Stourbridge, Cannock Chase, and Sutton Park to Lichfield. At all these places it is seen as a remarkable mass of rounded pebbles—mostly yellow, brown, or liver-coloured quartzites—and attains a thickness of 300 feet at Cannock Chase. West of Stourbridge the Conglomerate forms the “Ridge,” and caps Kinver Edge, dipping east or south-east at from five to eight degrees. Thence it is traceable northward by Upper Penn and Bushbury to Cannock Chase, where it forms a wide undulating heathy moorland, six miles in breadth from Bednall on the west to Rugeley on the east, and is exposed in many gravel pits and other excavations. The Staffordshire Coalfield lies like a great wedge between the Trias on its western and eastern sides. Crossing over from Stourbridge, we again find the Bunter Conglomerate or Pebble-beds extending between Harborne and Smethwick, and thence it runs northward in a broad band across the western suburbs of Birmingham, by Winson Green, Handsworth, Perry Barr, and Perry, to Sutton Park (where its outcrop is 3½ miles wide), and on to Aldridge, Wreford, Hopwas Wood, and Lichfield Racecourse. All along this line the Pebble-beds rest on Permian marls, and their thickness at Barr Beacon is about 400 feet. Good sections of the pebble-beds are rare on the south-west or west of Birmingham, but in the north-west they are well seen in a quarry south of Great Barr Station, and in one or two sections near the Beacon. At Sutton, exposures along the new railway lines to Lichfield and to Walsall have been numerous and good, and the Quarry in the Park, close to Blackroot Pool, gives a vertical section of thirty feet. Each section shows a mass of well-rounded hard pebbles, which have been so pressed together during the earth-movements that have taken place since their deposition that many are cracked, while all bear white indentations. The Bunter Conglomerate contains no fossils of contemporaneous age, but many species of shells have been obtained from the hard, rounded lumps of rock of which it is composed. These fossils being of necessity of the age of the rock-fragments in which they are included, they furnish a clue to the sources from which the pebble-beds were derived. The following list of these derivative fossils will give some idea of the results which have already been obtained:—

The Upper Red and Mottled Sandstone.—Stourbridge stands on the bright red sands of this division, which extend northward through Kingswinford to Trysall and Tettenhall. South of Birmingham we find the same strata at Harborne Heath and Mill—there is a good exposure underneath the drift in Flavel’s brick pit at “California”—from which point we can trace the “Upper Mottled” across the western part of Birmingham, by Rotton Park Reservoir and the Botanical Gardens; the beautiful soft red sandstone forming a strip about a mile in width between Spring Hill, Hockley Brook, Aston Villa, and Birchfields on the west, to the foot of Snow Hill, and Aston Park on the east. In the cemetery adjoining the Great Western Station at Hockley, there is a grand section, forty feet in height, where the incoherent sand is largely worked for moulding and foundry purposes. It is also exposed in and round Aston Park.

The Lower Keuper Sandstone.—The lower member of the Keuper is the most consolidated part of the Triassic formation, being best known as a tolerably hard sandstone, white or pink in colour, which often yields good building stone.

The “basement beds” of the Keuper are certain coarse sandstones and chocolate coloured marls seen in a pit at “California,” near Harborne. Above these come massively-bedded sandstones, of which there is a good exposure in the now disused quarry at Weoley Castle.

Commencing at Edgbaston, we can trace the Lower Keuper Sandstone by the Five Ways, and across the central highest part of Birmingham to Nechells, Gravelly Hill, and Erdington. Its lower boundary line, where it reposes on the Bunter, may be indicated by a line drawn from the junction of Monument Road with Hagley Road to the bottom of Snow Hill, and thence to Aston Station. From this point it extends eastward, for from one mile (Edgbaston) to half-a-mile (Aston). The ridge on which stands the Town Hall, St. Philip’s Church, &c., (475 feet above sea-level) is formed by the Lower Keuper Sandstone, and deep excavations for foundations in the centre of the town, frequently disclose the thin-bedded, dull-coloured, pinkish sandstones (known to workmen as “skerry”) which constitute the upper portion of this rock. Its thickness under Birmingham may be estimated at 200 feet. The average dip is from three to five degrees south-east. Similar beds are exposed in the cutting at Bromsgrove Railway Station, and it was from a quarry here (now closed) that the remarkable fossil fish was obtained, which was described by Sir Philip Egerton as Dipteronotus cyphus. From quarries at Coton End, Guy’s Cliff, Cubbington and Blakedown Hill, near Warwick, bones and teeth of four species of the Labyrinthodon have been obtained, and foot-prints of the same creature have been found in the Lower Keuper Sandstone in many localities.

The Keuper Red Marl is the uppermost member of the Trias. Near Birmingham it is abruptly separated from the Lower Keuper Sandstone by a line of fault, which can be traced from Selly Oak northwards to the junction of the Rea with the Tame. East of this line of fault, the red marls extend for ten or twelve miles forming an undulating fertile plain, on which stand Moseley, Smallheath, and Castle Bromwich, Coleshill and Whitacre. The thickness of the Keuper Marls is considerable. A boring in Smallheath Park was made to a depth of 440 feet entirely in such strata; but quite lately another boring at King’s Heath has been continued to a depth of 700 feet. Gypsum is plentiful in the red marls, occurring in white fibrous layers, but not of sufficient thickness to be of any value in this district. At Droitwich (eighteen miles south-west of Birmingham) the Keuper Marls contain a thick bed of rock salt, which yields an inexhaustible supply of brine.

The Upper Keuper Sandstone is a thin band of sandstone, not exceeding thirty feet in thickness, which occurs irregularly in the upper part of the Keuper Marls. It is well exposed at the entrance to the canal tunnel at Shrewley Common, and in a small quarry at Rowington (thirteen miles south-east of Birmingham), and also crops out on the hill sides at many points in South Warwickshire. From this thin stratum, the Rev. P. B. Brodie, F.G.S., has obtained a fossil fish (PalÆoniscus superstes), and the crustacean (Estheria minuta). Specimens of these may be seen in the Warwick Museum, which contains the finest collection of Triassic fossils possessed by any provincial museum.

How the Triassic Rocks were formed.—According to the writer’s views, the area now occupied by central England, alternated in condition during the Carboniferous epoch, between a low plain and a shallow sea. In the Permian period, land conditions prevailed, except in the North and North Midland Counties, where a brackish sea somewhat like the Baltic, it may be—occupied a shallow depression. In Triassic times this central sea appears to have been completely cut off from the open ocean, and to have formed a large inland lake, comparable to the Caspian or the Dead Sea of our own day. The southern boundary of this inland sea was formed by a ridge of old rocks which extended from Charnwood by Hartshill and the Lickey to the Wrekin and Malvern Hills. In the basin north of this axial ridge, all the subdivisions of the Bunter and the Keuper were in turn deposited; and the cliffs and reefs of the PalÆozoic rocks of which this coastline was composed, yielded large contributions to the pebble-beds, sands and marls, which constitute the Trias. According to a theory originally advanced by Professor Hull, and ably supported by Professor Bonney, the pebbles of the Bunter were mainly derived from the Paleozoic Rocks of the N.W. and N.E., some being possibly furnished by the ancient strata of N.W. Scotland.

The waters of the Triassic sea were so overcharged with salts of iron, that every grain of sand was encrusted, before its deposition, with a pellicle of peroxide of iron: of chloride of sodium (common salt) and sulphate of sodium (gypsum), there was also an excess, so that much was deposited on the sea-floor, producing beds of rock-salt and of gypsum, of considerable thickness. The presence of these mineral substances in the water was prejudicial to life, so that—as in the Dead Sea, and in Lake Utah to-day—few living creatures could inhabit the Triassic sea, and fossils are consequently of extreme rarity in strata of this age.

The Trias as a source of Water Supply.—The Triassic strata are so porous, that they absorb a large proportion of the rain which falls upon them, and they consequently form an underground reservoir which, when tapped by wells or boreholes, is capable of yielding an almost inexhaustible supply of good, though somewhat hard water. In this way Birmingham receives three-fourths of its water from three deep wells—two on the north-east of the town, at Aston and at Perry respectively, and one on the south-west, near Selly Oak. These wells extend to depths of 400 feet, passing through the Upper Mottled Sandstone, and piercing the pebble beds, and the average supply of water from each is three million gallons per day. The hardness varies from nine to fifteen degrees. There are many other deep wells in and round the West of Birmingham, and at Stourbridge, Wolverhampton, etc., which derive their water from the same source.

Liassic and RhÆtic.

BY REV. P. B. BRODIE, M.A., F.G.S.

The Lias occupies a large area in the south and east of the Birmingham District, and consists for the most part of the middle and lower divisions. The highest position of the Lias is seen on the south and south-eastern division of Warwickshire, the middle Lias forms the hills projecting in spurs to the north-west, and the lower division extending in the same direction, at a lower level, up to the southern edge of the Trias.

Upper Lias.—The Upper Lias is chiefly represented by a thin bed of clay, with some characteristic fossils. It occurs on the hills of Fenny Compton and elsewhere, and there is evidence to show that it formerly capped the range of the Edge Hills adjacent, occupying its natural position above the marlstone, or Middle Lias, of which they are mainly composed. From Fenny Compton to Harbury, a good descending section may be obtained from the marlstone (rock bed), through the underlying clays and marly beds, through the “Lima Beds” and White Lias, to the New Red Marls at Harbury.

Marlstone or Middle Lias.—The Marlstone (rock bed) is largely quarried on the Avon and Burton Dassett Hills. It forms a good building stone, more or less indurated, of a green or yellow brown colour, sometimes ferruginous. It forms a conspicuous range of hills of moderate height of which Edge Hill is the highest, from which it strikes southward towards Oxfordshire. The plain below is occupied by the underlying division of the Lower Lias. In this county the marlstone contains very few fossils, and those chiefly brachiopodous shells belonging to the genus Terebratula. In most cases elsewhere the Marlstone proper, or highest zone, is very fossiliferous, and abounds in marine shells, which are usually well preserved. The sandy beds immediately below are rarely exposed, but crop out in a lane near Bitham House, where as usual they contain many fossils. The inferior clays and marls are not visible except in some brick pits near Fenny Compton and along the line of railway. These are very full of fossils in the zone of Ammonites Jamiesoni and Ibex, here nearly one hundred feet thick, and especially at one horizon in a coarse, hard, stony band which contains numerous corals towards the upper part of the cutting, near the station.

Lower Lias.—For the most part this formation spreads over the portion of the country on the north-east, east, south-east, south and south-west of Warwick. A remarkably fine section is exposed in the railway cutting near Harbury Station. This portion of the series is also largely quarried at Rugby, and in other places south and south-east of Stratford. The strata consist of beds of blue clay or shale interstratified with beds of blue rubbly and argillaceous limestone, much quarried for hydraulic lime. One good section of the lime-yielding beds occurs at Messrs. Greaves and Lakin’s Quarries at Stockton and Harbury. The lowest zones of the Lias are largely quarried at Wilmcote, and may be seen at the remarkable outlier of Brown’s Wood, near Henley-in-Arden, and at another (Copt Heath), near Knowle. These two last are of special interest, because they shew the lowest beds of the Lias (in connection with and passing into the RhÆtics,) resting immediately upon the New Red Marls. The thickness of the Lower Lias in the county is above 600 feet; but only the inferior zones of Ammonites angulatus and A. planorbis are laid open to any great extent. The best sections of the Lima beds (A. angulatus zone) occur in the railway cutting at Harbury, Stockton lime quarries, and the extensive quarries at Newbold near Rugby. Fossils are not very numerous, but the following occur:—Gryphea incurva, Rhynchonella variabilis, Ammonites angulatus, Pecten, various species, Lima gigantea, and bones and teeth of Plesiosaurus and Ichthyosaurus. Fish are comparatively rare, two or three only were found at Harbury and a very few near Rugby.

The higher ground round Wilmcote and Binton is also capped by these Lima beds; but the district is more or less affected by small faults, so that certain beds in one contiguous quarry are absent in another. The lower limestones (insect beds) are largely worked in this locality, and are of much economical value. With the exception of remains of insects and fragments of plants, the fossils are entirely marine, Ammonites planorbis and A. Johnstoni, being abundant and characteristic. Crustacea belonging to the genera Astacus and Eryon, the latter of great size are not unfrequently met with. Small fishes, Pholidophorus Stricklandi, and the larger Dapedium and Tetragonolepis more rarely occur. A fine example of the latter is preserved in the Warwick Museum. The large Enaliosaurians are well represented by some fine specimens of Ichthyosaurus and Plesiosaurus; the P. megacephalus in the Museum at Warwick being nearly entire, measuring 14 feet 4 inches in length. Large masses of driftwood and a few fronds of ferns are sometimes met with. But perhaps the most interesting and remarkable fossils are the insects. Twenty-four families and genera were determined more than twenty years ago, since which time many important additions have been made. The Coleoptera and Neuroptera are most numerous. Small beetles are not unfrequently found entire. Among these may be noted the families BuprestidÆ, ElateridÆ, CarabidÆ, and others.

There are also remains of Orthoptera, Homoptera, LibellulidÆ, and some Diptera. Many of the Neuroptera were evidently of gigantic proportions, but most of the insects were of small size, and like the associated plants, are indicative of a temperate climate. They are most nearly allied to forms which now inhabit North America. There are few extinct or unknown genera among them.

RhÆtic Series.—The highest beds referred to this series consist of certain hard, fine grained limestones, which, from their ordinary white colour, have been termed White Lias. They occupy a considerable area south and south-east of Warwick. They constitute a purely local deposit, and are confined for the most part to this county and Somersetshire. They are often close-grained and hard limestones, and make a useful building material and a good lime. Their colour is mostly white, with a yellow tinge, and occasionally pink and grey. Some geologists consider these beds to belong to the “RhÆtic Series,” others to the passage beds between the Lias and the latter, while others still class them with the Lias.

The undisputed RhÆtic rocks lie between the White Lias and the Triassic Marls. In Warwickshire they are rarely exposed, and then much reduced in bulk, compared with their development in Gloucester and Glamorgan. They may be seen to a limited extent below the White Lias in the railway cutting at Harbury, where a band of yellowish sandstone contains the small bivalved crustacean, Estheria minuta; and also at the small outlier of Brown’s Wood, and at Stooper’s Wood, near Wooton Wawen, where this sandstone occurs with inferior shelly limestones and sandy bands, containing the usual RhÆtic fossils, e.g., Cardium RhÆticum, Avicula contorta, Pleurophorus elongatus, Pecten valoniensis, and Schizodus cloacinus. The nearest exposure of the RhÆtic to Birmingham occurs round the fringe of an outlier of Lower Lias resting on the Upper Red Marl near the village of Knowle. This outlier is about a mile and a half long, by half a mile broad. Its highest beds at Copt Heath contain Ammonites planorbis. The beds referred to the RhÆtic include a stratum of yellow micaceous sandstone full of Schizodus cloacinus, which, though usually in the form of casts, is sharp and well defined. The bone bed, though no where exposed, is probably present in its normal position. A fine section, with numerous characteristic RhÆtic fossils was exposed on the railway cutting at Summer Hill, between Stratford and Alcester. RhÆtic black shales were passed through at Snitterfield, in making a tunnel in connection with the new reservoir for Stratford.

Glacial and Post Tertiary Deposits.

BY H. W. CROSSKEY, LL.D., F.G.S.

Post Tertiary Deposits are scattered profusely over the district of which Birmingham is the centre, and present many problems of too complicated a character to be discussed in the pages of this guide. It must suffice to indicate a few of their chief exposures and characteristics. The term “Boulder Clay” is used in this note to denote a clay shown to be connected with the Glacial epoch, by containing a greater or less number of erratic blocks; and in the employment of the term, no theory regarding the method of formation of the deposit will be implied.

The Post Tertiary deposits of the district may be arranged in the following general order:—

The most complete section that has been found is at “California,” near Harborne.

Resting upon the Bunter Sandstone, about 480 feet above the sea level, is a Lower boulder clay, containing erratic boulders of slate, felsite, quartzite, intermixed with blocks and stones of local origin. Many of the erratics are angular, and some (especially the slates) are finely striated. The whole deposit is unstratified and compact, and the boulders are roughly pressed together, in every variety of position, without any orderly arrangement. This boulder clay is succeeded by the Middle Sands and Gravels which are irregularly stratified and show false bedding. Fragments of coal occur among the pebbles. The sands and gravels dip rapidly to the S.W., and pass under an Upper boulder clay. The Upper Boulder Clay consists of a compact mass of clay with erratics scattered through it; but the erratics are neither so abundant nor so confusedly pressed together as in the lower bed. Granite has been found, although rarely, associated with the travelled felsites and quartzites, together with a few flints; and local stones and blocks are also mixed up with the clay—the clay itself however largely preponderating and being available for brick making.

The series is capped by a mixture of clay, sand, and gravel in varying proportions, which fills many hollows that have been washed out of the upper clay; and must be regarded as Post Glacial. Taking the general divisions indicated by the California section, attention may be directed to the following illustrative facts and sections. Glacial striÆ upon the surface of the rock have been noticed at Weoley Hill Quarry close to California. The removal of a mass of clay, sand, and gravel exposed a distinctly striated surface of hardened Bunter Sandstone. The polished surface dips towards the south west, in which direction the principal striÆ run, although there are several cross striÆ. The complete section shews (a) striated and polished Bunter (altitude 520 feet above sea level); (b) thin bed of marl; (c) sands and gravels (Middle Glacial); (d) clay (Upper Boulder Clay).

A very large number of well-marked and finely smoothed and polished grooves occur upon the blocks of native rock which are strewn over the irregularly shaped mass of basalt constituting Rowley Hill, Worcestershire. Isolated grooved blocks rest upon the surface of the hill, having been carried by external force into their present position; but there is also, at Rowley Hall Quarry, a kind of platform, capping the solid mass of basalt, which is almost entirely composed of blocks with smoothed and grooved surfaces, stiffly imbedded in clay.

The question has been raised whether, since the basalt readily develops joints, these grooves may not be rudimentary joints, or whether disintegration may not have taken place along certain lines which have gradually become grooves. I entertain no doubt, however, of their glacial origin. No other explanation than that the grooves were the work of moving ice can account, I think, for their excellent polish, their frequent parallelism, their adaptation to the hollows and protuberances of the blocks they cross, and their predominant trend from north-east to south-west. The absence of erratics from the boulder clay in which the grooved basaltic blocks are embedded is evidence of local ice action at Rowley Hill. It is notable also that angular blocks of basalt from Rowley Hill have been found in Birmingham, blocks which must have travelled at least six miles.

It is often difficult to decide the precise age of the boulder clays of the district; and whether any individual bed is referred to the upper or the lower series is more dependent upon the glacial theories that may be adopted than upon any observations that can be made in the field. A Boulder Clay, of a typical kind, has been exposed at a brickyard, at the bottom of Oak Street, Wolverhampton. This clay contains an extraordinary number and variety of erratic blocks, without question from the Lake District and south of Scotland, a few flints, together with pebbles from the Bunter beds. One of the sides of a boulder of felsite, measuring 11 × 3 × 3ft., is flat and smooth, and covered with parallel striÆ. The sands and gravels rising in small hillocks near the Cemetery, and slightly covering the clay of the pit, are probably Middle glacial. A boulder clay, formerly exposed at Icknield Street, Birmingham, while presenting the same physical characteristics as the Wolverhampton clay, differed from it widely in the nature of the embedded erratic blocks. Instead of having travelled from the Lake District or Scotland, a large proportion were derived from rocks that occur in situ at the Berwyn and Arenig Hills. The condition of the New Red Sandstone ridge, against which this boulder clay rested, was remarkable. The sandstone rock was broken up, and large fragments of it were lifted out of their position and thrust into the middle of the drift.

The changes of level which occurred during the glacial epoch are shown by the deposits at Frankley Hill. In the clays and sands cut through by the Halesowen Railway only a few erratics (felsites) were found; but on the summit of the section they are abundant and of large size (e.g., 4 × 4 × 2ft.) Professor Bonney, who has examined them, feels certain they must have come from Wales, having seen nothing like them in the Lake District. Their height is nearly 800ft. above the sea level. Were these erratics brought by land ice, the alteration in the physical geography of the country must have been enormous to have enabled a glacier to have moved downwards over this point; were they dropped from icebergs, the land must have been depressed to the extent of at least 900ft., to form a sea in which the bergs could have floated.

Turning to the Middle Glacial Clays, Sands, and Gravels, these may be seen more or less developed in almost every section cut through undulating ground; and they are occasionally twisted and contorted. In the immediate neighbourhood of Birmingham they are not fossiliferous.

At Ketley, near Wellington (Shropshire) however, fossiliferous sands and gravels occur, which I am inclined (provisionally) to assign to this period. They rest upon a bed containing erratic blocks of granite, and other rocks of northern origin; and I collected from them 13 species of mollusca. Only one species was peculiarly northern (astarte borealis) but all in the group have an arctic range of habitat. The elevation of these beds is about 357 feet above the sea.

At Fox Hall Field, New Lodge, Lilleshall (Shropshire) in a pit worked for sand, 463 feet above the sea, Mr. Woodward discovered 21 species of mollusca, three—viz., Dentalium abyssorum, Natica affinis, and Astarte borealis—being characteristically arctic and extinct in British waters.

The Upper Boulder Clay is worked for bricks in many localities. It is distinguished from the Lower Boulder Clay, by having erractic blocks sparsely scattered through it. It is often very compact and tenacious. No fossils have as yet been found in it; unless indeed a clay derived from a drain in a street at Wolverhampton, in which I detected fragments of Tellina balthica, the spine of an Echinus, Polymorphina lactea, and Polystomella crispa, may be assigned to this division of the epoch.

The extraordinary dispersion of erratic blocks over the surface of the ground remains to be noticed, and constitutes one of the most remarkable phenomena in local glacial geology. I distinguish the boulders resting on the surface of the ground from those embedded in the clay beds, although it is of course possible and probable that the clay has been largely denuded, and the boulders have thus been left exposed. Many of these erratic blocks may therefore belong to the Lower Boulder Clay; while others may have fallen from the icebergs which during the proved subsidence of the land must have floated over the “Midland” sea, and have been deposited in the Upper boulder clay, while it was in process of accumulation.

How far the dispersion of erratics over the Midlands may be referred to the ice sheet of some geologists, or to the icebergs of the Archipelago period in the history of Great Britain, must, at present, be regarded as an open question.

The Midland erratics have undoubtedly travelled from three distinct regions, viz., (1) from Wales, (2) the western part of the Lake district, and (3) Kirkcudbrightshire. Boulders from the more easterly part of the Lake district, such as the Snap granite boulders, so abundantly spread over Yorkshire, have not been found in this neighbourhood.

The peculiar distribution of the Midland erratics is noteworthy. Commencing at Bushbury Hill (a little to the north of Wolverhampton, on the table land facing towards the N.W.) the Lake rocks and the Scotch rocks—Criffell granites and Eskdale granites—are largely intermingled. Journeying westwards, a stream of boulders from Wales crosses the northern streams. On and around the Clent Hills (1023 feet) south west of Birmingham, Welsh felsites are the only boulders to be found. Birmingham itself being in the rear of the higher part of the table land on which it stands, is in a kind of protected district, so far as the northern stream of boulders is concerned, and the erratics in its immediate vicinity are chiefly Welsh felsites; a few fragments however of granite are occasionally found.

Post Glacial Beds.—The most complete section of post glacial beds in this locality was obtained during excavations made at Shustoke, near Birmingham; when a bed of black peat, containing the remains of Elephas antiquus, Cervus elephas, and Bos primigenius, with hazel nuts and fragments of wood, was discovered 7ft. 6in. beneath the surface. The section was as follows:—

The fossils found in the peat have been placed in the Geological Museum of the Mason College.

PETROGRAPHY.
Notes on the Igneous and Metamorphic Rocks of the Birmingham District.

BY S. ALLPORT, F.G.S.

The space available for some account of the crystalline rocks being strictly limited, it would be useless to attempt anything more than a brief general description of the most important and interesting varieties. Fortunately there is abundance of material, for Birmingham, as a central point, affords unusual facilities for the study of this branch of petrology. Although the rocks here described appear to be scattered over a rather wide area, it will be found that every locality mentioned may not only be easily reached from one of the railway stations, but that a good series of specimens may be collected and the return journey made within the same day.

The Malvern Hills.—It was clearly shown by Dr. Holl, in 1865, (Quar. Jour. Geol. Soc., Vol. xxi.) that the central portion or axis of this chain of hills consists of a great series of true crystalline schists, among which the prevailing types are hornblendic and micaceous gneiss, hornblende-schist, mica-schist, and a quartzo-felspathic rock, all of which are more or less distinctly foliated. There is, however, great variety in the relative proportions of the constituents; in many places either the hornblende or the mica are nearly, or even quite absent; the felspar and quartz then form the mass of the rock. In the quarries on the east side of the North Hill, beautiful examples of hornblende and felspar rock are abundant; they contain more or less quartz, with a little mica, and occasionally pass by insensible gradations from a well-marked gneissic structure into a coarsely crystalline mass in which foliation is no longer apparent. These latter are, however, exceptional cases, and there can, I think, be no doubt that we have here, in the Midlands, a considerable exposure of the oldest type of foliated crystalline schists, or as they are now frequently called Pre-Cambrian or ArchÆan rocks. The rocks of the North Hill are probably the oldest; they have been much disturbed, and are generally the most coarsely crystalline of the series. The more basic portions have suffered a considerable amount of alteration; the secondary constituents, chlorite and epidote, become abundant, and occasionally the hornblende has been completely replaced by the latter mineral; the rock then becomes an epidote schist of a pale-yellowish colour. In Swinyards Hill there is a micaceous gneiss with garnets, and in Raggedstone Hill there are interesting varieties of contorted mica-schist containing a large proportion of quartz. Dykes of intrusive rocks occur in nearly all the hills, but become far more numerous towards the north; they are very uniform in appearance, and are probably altered dolerites or diorites; very few specimens have been examined, and they belong to the former group. In the North Hill there are some masses of true diorite, but their relation to the hornblendic gneisses with which they are associated has not been clearly established.

Mount Sorrel Granite.—The granite is of two varieties, red and grey, the difference being due to the fact, that in the red masses, the partially decomposed felspar has been coloured by ferric oxide. The rock is a hornblendic granite, the constituents being quartz, felspar, biotite, hornblende and titanite, with magnetite and a little apatite. The felspars are orthoclase and plagioclase; the former is much decomposed, while the plagioclase frequently remains clear, and exhibits well its twin striation. Biotite was originally abundant, but is very frequently replaced by a clear green substance, which is strongly dichroic, the two colours being grass-green, and clear yellow. The hornblende has been greatly decomposed; clear crystals are, however, not uncommon, and exhibit the usual optical characters of the mineral. The products of alteration are chlorite and epidote. The titanite appears in reddish-brown grains, but is not very abundant. In 1879, the writer discovered the junction of the granite with the sedimentary rocks, and proved that the former was intrusive (Geol. Mag. dec. ii., Vol. vi., p. 181). The junction occurs in Brazil Wood, where there is a small quarry, in which granite veins may be seen to penetrate the strata in various directions; a large mass of granite is also within a few yards. Some of the phenomena of contact metamorphism may here be readily studied, the granite having converted the slate into a crystalline micaceous schist, quite similar in character to those produced under like conditions round the granite in Cornwall and elsewhere. Small garnets occur in the altered slates, and also in the granite close to the junction.

The Charnwood Syenites.—The Syenites and other igneous rocks of Charnwood, have been described by Messrs. Hill and Bonney (Quar. Jour. Geol. Soc. Vol. xxxiv., p. 199.) The original constituents are felspar, hornblende, quartz, apatite, ilmenite, magnetite and titanite. The felspar is of two kinds, orthoclase and plagioclase, the former is very turbid and decomposed, while the plagioclase is clear, and retains its usual optical characters. The curious intercrystallization of quartz and felspar, known as micropegmatite, is common in the masses of syenite near Groby; the best examples, however, have been found by the writer in the Markfield rock, where it appears to form a ground-mass in which the larger crystals of orthoclase and plagioclase are enclosed. A small portion of the hornblende is still characteristic, but the greater portion appears in various stages of decomposition; the alteration products being chlorite and epidote. Titanite is by no means rare, and occurs in well formed twin crystals.

Diorites of Atherstone and Nuneaton.—A careful examination of many specimens collected by the writer from the various masses marked in the map 63 S.W. of the Geological Survey shows clearly that they are diorites, the characteristic constituents being hornblende and a triclinic felspar; these minerals, together with magnetite and apatite are invariably present, and in addition, a little orthoclase is seldom absent. The best specimen examined is from a quarry near Marston Jabet; it is a fine-grained rock, similar to a basalt in external appearance, but contains numerous crystals of hornblende and plagioclase which are generally quite unaltered. The clear brown crystals of hornblende are unusually well developed, and afford excellent opportunities of examining their crystallographic and optical characters. There are also present many grains of magnetite, and a few needles of apatite. The only product of alteration is a little calcite in the spaces between the crystals. Other specimens from the same quarry will perhaps give a better idea of the general character of the rocks of the district, and they possess a special interest, as they afford unusually good examples of successive stages of alteration. In one specimen the constituents are well preserved, the plagioclase is clear and exhibits its characteristic twin striation; the hornblende is, for the most part, unaltered, but is much fissured, and occasionally contains so many cavities that the crystals are little more than skeletons. A ground-mass in which the constituents were set has been highly altered, and now consists of a fine granular substance, partly serpentinous, with here and there a little calcite. A second example is quite similar in texture to the last; the felspar, still recognisable as triclinic, has been partially converted into a grey turbid substance. The hornblende occurs in various stages of alteration; some crystals are but slightly attacked, while others are to a considerable extent replaced by a pale green serpentinous substance. The alteration has followed the cleavage-lines and fractures, while the numerous cavities just mentioned are also filled by the same substance. In a single slice there may be seen almost every degree of change from a slight marginal erosion to a mere skeleton of the original. Of the latter, however, some little is always left; and whether the alteration be little or great, the crystalline forms are perfectly preserved. In a third specimen the alteration has proceeded still further, the whole of the hornblende crystals having been completely converted into pale green pseudomorphs; they were originally large and well developed, and their forms are still perfectly sharp and distinct. The felspar is here quite turbid and opaque, and the interstitial ground-mass is represented by calcite.

Purley Park, near Atherstone.—The rock here contains, in addition to the usual brown hornblende, many crystals and grains of clear yellowish augite, and several pseudomorphs after olivine. The augite crystals exhibit the usual forms, some being twins. The pseudomorphs after olivine are quite similar to others observed in certain highly altered dolerites, they consist of calcite or calcite and viridite; they are numerous, and are generally larger than the crystals of augite or hornblende.

Quarry close to Atherstone.—This rock also contains both augite and hornblende; and lastly, in the railway cutting at Chilvers Coton, several interesting varieties of diorite may be found.

The Rhyolites of the Wrekin near Wellington, Shropshire.—In the large quarry in Lawrence Hill, at the north end of the Wrekin, and at Lea Rock on the Shrewsbury Road, are to be found some of the most beautiful varieties of ancient volcanic glassy rocks hitherto discovered in Britain. The rocks in their present condition do not look like glass, owing to a process of devitrification, which they have evidently undergone. There can, however, be no room for doubt as to their original vitreous condition, for they exhibit, under the microscope, certain peculiar perlitic and spherulitic varieties of structure, associated with characteristic forms of microliths, which are found only in the pitchstone and obsidian varieties of volcanic glass. In the quarry in Lawrence Hill, thick beds of volcanic ashes and agglomerates are to be seen dipping towards the north at a high angle, and an examination of this hill and the Wrekin shows that they both consist of a series of stratified ashes alternating with several flows of rhyolite. One of the ash beds contains numerous spheroidal blocks of thoroughly characteristic varieties of glassy rocks; they have not yet been described, but it may here be stated that, in addition to many typical varieties of known rhyolites, there are also included among them some of the rarer glassy kinds described by Zirkel in his Petrography of the 40th Parallel. Beautiful examples of the spherulitic and perlitic varieties may be found at Lea Rock, and have been described by the writer in the Quar. Jour. Geol. Soc. Vol. xxxiii., p. 449. It has been shown by Dr. Callaway, that all these rhyolites are of Pre-Cambrian age; we have here, therefore, the clearest proof that, during very early geological periods volcanic action was of the same kind, and produced the same results, as in more recent times.

South Staffordshire.—The igneous rocks of the South Staffordshire coalfield belong to the basic series, and are, without exception, dolerites or basalts, the latter being merely a fine grained variety of the former. They have been intruded among the coal measures and shales, and are frequently found in an excellent state of preservation. The original mineral constituents are crystals, or crystalline grains of triclinic felspar, augite, olivine, magnetite, ilmenite, and apatite. These minerals are very frequently quite unaltered, with the exception of the olivine, which is often partly converted into serpentine; this is the pale green substance seen along the cracks, and around the sides of the grains; generally, however, the decomposition has been continued until the formation of complete serpentinous pseudomorphs after olivine has been the result. The Hailstone Hill, near Rowley Church, is the best locality for varieties in texture and composition, as also for contemporaneous veins. In the large quarry there is a very coarsely crystalline variety containing large flat plates of ilmenite, and here also may be found some light-coloured veins in which orthoclase is the predominant felspar. The writer has also found in the same quarry vessicular and amygdaloidal varieties of the rock. It need scarcely be mentioned that, minute details of structure and composition can only be studied in thin slices under the microscope. Rocks of similar character to the above occur in the following localities:—Pouk Hill, near Walsall; Titterston Clee Hill (sheet 55, N.W.), Knowl Hill, near Kinlet (sheet 55, N.E.), and Swinnerton Park, eight miles N.E. of Stafford. For fuller descriptions of these rocks, see Allport, Quart. Jour. Geol. Soc., Vol. xxx., p. 529.

Mining Statistics of the South Staffordshire Coalfield.

By PROFESSOR W. E. BENTON, A.R.S.M., F.G.S.

Minerals Worked.—The principal minerals worked within the limits of the South Staffordshire Coalfield are coal, ironstone, and fireclay from the Carboniferous formations, and limestone from the underlying Silurian rocks.

The Coal is bituminous, non-caking, and much of it contains a high percentage of water and oxygen. Some of the seams produce excellent house-coal, others manufacturing and steam coal.

The Ironstone is an argillaceous carbonate of iron, occurring as nodules in the roofs of the coal seams, or as thin beds within them.

The Fireclay, particularly in the neighbourhood of Stourbridge, has a high refractory power.

Quantity of Minerals Raised.—The annual produce of minerals during the last twenty years has remained without any considerable alteration. The Government Mineral Statistics for 1885 are not yet published, but in 1884 the quantities of minerals raised in South Staffordshire Coalfield were:—Coal, 9,688,047 tons; ironstone, 116,951 tons; fireclay, 205,320 tons; limestone (no statistics given). The respective values of these minerals at the mines were estimated at:—coal, £2,785,313; ironstone, £62,974; fireclay, £42,781.

The total number of persons employed at the mines during the same period was 23,782.

Destination of the Minerals.—The greater part of the coal is consumed in the district for house purposes, for steam raising, for the manufacture of bricks, pottery, glass, salt, &c. The remainder is carried out of the coalfield into the south and south-western districts of England by the London and North Western, Great Western, and Midland Railway Companies, for house and steam purposes. The gas coals and coke used in the Birmingham district are not the product of the South Staffordshire Coalmeasures, but are brought principally from North Staffordshire, Derbyshire, and Yorkshire.

The whole of the ironstone raised is smelted within the district, in addition to large quantities of iron ore (hydrated oxide) brought from the Northampton and North Staffordshire mines. The manufacture of pig iron has within the last decade decreased to such an extent that less than one-third of the existing furnaces of South Staffordshire are at present in blast.

The quantity of pig produced in the coalfield in 1884, was 356,873 tons; in the reduction of which 810,936 tons of coal (including coal converted into coke) were used, or about 45½ cwts. of coal to one ton of pig iron. The whole of the pig iron is retained in the district. The finished iron trade retains its importance, more than one-third of the existing puddling furnaces and rolling mills in Great Britain occur within the limits of the South Staffordshire Coalfield.

The finished iron is produced from local pig iron, and from pig iron brought from Derbyshire, Yorkshire, and North Staffordshire. The steel production in South Staffordshire is gradually increasing. The processes adopted are those known as the Bessemer, Gilchrist and open hearth.

The South Staffordshire fireclay is worked principally in the neighbourhood of Brettle Lane and Stourbridge, and is employed in the production of firebricks, gas retorts, pottery, etc. Much also is conveyed into other districts in a raw condition for pottery purposes.

The Silurian limestone is worked partly in open work in the neighbourhood of Dudley, and partly by ordinary underground mining operations at the Wren’s Nest, Sedgley, and at Walsall.

Characteristic Features of the Mining of South Staffordshire.—There are several noteworthy features in the mining of South Staffordshire. A stranger is especially impressed with the large number of separate collieries in working (about 600) in proportion to the quantity of mineral raised. This peculiarity is due essentially to the insignificant depth at which the minerals occur below the surface (indeed, at Foxyard, near Tipton, coal has long been quarried in an outcrop of the 10 yard seam). This “Shallow Mining” has passed its meridian. The future mining of the district is forecast by those remarkable operations on the “red ground,” forming the eastern side of the coalfield. The most recently opened seam in the red ground is at Hampstead, three miles north of Birmingham, where coal mining is carried on below the Permian and Triassic, at a depth of more than 600 yards.

Another feature of the mining is the unique South Staffordshire mode of getting coal in the ten yard seam, called “Square Work.” This method has met with much condemnation from strangers, but after trial of other methods, it still dominates. A further and most strongly marked peculiarity of the South Staffordshire area is the tendency of some of the Black Country coals to spontaneous ignition. Much coal has thus in times past been sacrificed; but a better acquaintance with the causes of this phenomenon has led to measures which have reduced and which must still further reduce this sacrifice of wealth.

Mines’ Drainage.—In the Tipton and Old Hill districts many of the coal mines are water-logged. In 1873 a Parliamentary Commission however was appointed to drain this area, and was empowered to levy rates to defray the drainage expenses. The drainage area under the direction of this Mines’ Drainage Commission is 50 square miles. The principal pumping stations are the Moat, the Stoneheath Station, and the Bradley Station. The Bradley pumping engines (a quarter of a mile from Moxley on the Great Western Railway) are of the compound type having 52-inch and 90-inch steam cylinders. These engines, with a 10 feet stroke, and six strokes per minute, work two 27-inch plunger pumps, and raise from a depth of 126 yards more than 4,000,000 gallons of water per 24 hours. As a result of this gallant effort to recover these water-logged minerals, the number of pumping stations has been gradually reduced in the Tipton district from 77 in 1873 to 10 in 1885, and the quantity of water from 23,000,000 to 10,000,000 of gallons daily. To meet the inevitable expenses, a rate of 9d. per statute ton is levied on all coals, slack, and ironstone; 3d. per statute ton on all fireclay and limestone, and 1d. per statute ton for surface drainage on all minerals, raised in the Tipton district. In the Old Hill district a much lower mines’-drainage rate is collected.

LITERATURE.
Books, Papers and Maps bearing upon the Geology of the Birmingham District.

Fundamental Gneissic and Volcanic Rocks.

• Phillips, Prof., “On the Geology of the Malvern and Abberley Hills.” Memoirs of the Geological Survey, Vol. ii., 1848.
• Holl, Dr. H. B., “On the Geology and Structure of the Malvern Hills.” Quart. Journal Geol. Soc., Vol. xxi., p. 72.
• Callaway, Dr. C., “On a second Pre-Cambrian Group in the Malvern Hills.” Q. J. G. S., 1880, Nov. 1880.
• Prof. T. G. Bonney, LL.D., and Rev. W. Hill, M.A. “On the Pre-Carboniferous Rocks of Charnwood Forest.” Q. J. G. S., 1877, p. 754, &c.
• Allport. S., “Ancient Devitrified Pitchstones and Perlites from Lower Silurian District of Shropshire.” Quart. Journ. Geol. Soc., 1877, p. 439.
• Callaway, Dr. Chas., “The Pre-Cambrian Rocks of Shropshire.” Quart. Jour. Geol. Soc. 1879, p. 643; ibid, 1882, p. 120.

Cambrian Formations.

• Prof. Phillips, “Geology of Malvern and Abberley Hills.” See above.
• Holl, Dr. H., “Geology and Structure of the Malvern Hills.” See above.
• Callaway, Dr. C., “On a new Area of Upper Cambrian Rocks in South Shropshire.” Q. J. G. S., 1877. p. 652.
• T. S. Houghton., M.A., F.G.S. “Note on the Age of the Quartzite of the Lickey.” Proceedings Birmingham Philosophical Society, 1881-2, p. 206.
• Prof. C. Lapworth, “On the Discovery of Cambrian Rocks in the neighbourhood of Birmingham;” ibid, p. 234. See also Geological Magazine, 1882, p. 563; ibid, July, 1886.
• W. Jerome Harrison, F.G.S., “On the Pre-Carboniferous Floor of the Midlands.” Midland Naturalist, 1855, p. 38.

Silurian Rocks.

• Sir R. J. Murchison, “Silurian System,” p. 408, and 480.
• J. Beete Jukes, F.R.S. “The Geology of the South Staffordshire Coalfield.” 2nd Ed., p. 145 et seq.

Carboniferous Rocks.

• Sir R. J. Murchison, “Silurian System,” p. 463.
• J. Beete Jukes, F.R.S. “The Geology of the South Staffordshire Coalfields.” 2nd Edition; see also Jukes, “On the Geological Structure of South Staffordshire Coalfield.” Birmingham and Midland and Hardware District, 1866, p. 1.
• Howell, H., F.G.S., &c. “The Geology of the Warwickshire Coalfield.” Mem. Geol. Survey, 1859.

Permian and Triassic Rocks.

• Hull, Prof., M.A., F.R.S. “Triassic and Permian Rocks of the Midlands.” Memoirs Geol. Survey.
• Sir And. Ramsay, F.R.S., “On the occurrence of Angular boulders in the Permian Breccia of Shropshire and Worcestershire.” Quart. Jour. Geol. Soc., 1855, p. 185.
• Rev. P. B. Brodie, “Upper Keuper Sandstone of Warwickshire.” Journ. Geol. Soc., Vol. xii., p. 374.
• Prof. L. C. Miall, “Labyrinthodonts from the Keuper Sandstone, in the Warwick Museum.” Journ. Geol. Soc., Vol. xxx., p. 417.
• W. J. Harrison, “On the Quartzite Pebbles contained in the Triassic Strata of England, and on their Derivation from an Ancient Land Barrier in Central England.” Proc. Birmingham Phil. Soc., Vol. iii., p. 157.
• Prof. T. G. Bonney, “On the Pebbles in the Bunter Beds.” Geol. Mag. for 1880, p. 404.
• Thos. Davidson, “Brachiopoda of the Budleigh-Salterton Pebble Bed.” Q. J. G. S., Vol. xxvi., p. 70. 1870.

Liassic and RhÆtic Rocks.

• Rev. P. B. Brodie, “Lias Outliers at Knowle and Wooton Wawen.” Journ. Geol. Soc., Vol. xxi., p. 159. 1865.
• R. F. Tomes, “Corals of the Lias.” Journ. Geol. Soc., Vol. xxxiv., p. 179. 1878.
• W. J. Harrison, “The RhÆtic Section at Dunhampstead, near Droitwich.” Proc. Dudley Geol. Soc., Vol. iii., p. 115.

Glacial and Post Tertiary Formations.

• “The Direction and Limits of Dispersion, etc., of the Erratic Blocks of the West of England and East of Wales,” by D. Mackintosh, F.G.S. Quarterly Journal Geological Society, Vol. xxxv., p. 425.
• “The Correlation of the Drift Deposits of the N.W. of England, with those of the Midland and Eastern Counties,” by D. Mackintosh, ibid, Vol. xxxvi., p. 178.
• “Post Tertiary Beds of the Midland District,” by H. W. Crosskey, LL.D., and C. J. Woodward. Proceedings of the Birmingham Natural History Society, 1873, p. 43.
• “On a Section of Glacial Drift, recently exposed in Icknield Street, Birmingham.” By H. W. Crosskey. Proceedings of Philosophical Society of Birmingham. Vol. iii. p. 209.
• “The Grooved Blocks and Boulder Clays of Rowley Hill.” By H. W. Crosskey. Ibid, Vol. iii., p. 459; and Vol. iv., p. 69.
• “Reports of the Committee of the British Association on the Distribution, etc., of Erratic Blocks; drawn up by H. W. Crosskey.” 1873-1885.
• “The Geological Section along the West Suburban Railway from Birmingham to King’s Norton.” By F. W. Martin. Proceedings of Philosophical Society of Birmingham, Vol. iv., p. 257.

Petrography.

• S. Allport, F.G.S., “Diorites of E. Warwickshire Coalfield.” Q. J. G. S.
• S. Allport, F.G.S., “Carboniferous Dolerites.” Q. J. G. S., xxx., p. 529.
• S. Allport, F.G.S., “Vitreous Rocks of the Wrekin,” ibid, xxxiii., 449.
• See also the Papers by Professor Phillips, Dr. Holl, and Dr. C. Callaway, Rev. Professor Bonney and Rev. T. Hill, cited above.
• T. H. Waller, B.Sc., “Observations on the Structure of the Rowley Rag.” Midland Naturalist, 1885, p. 261.

Maps of Birmingham District.

Published by H.M. Geological Survey.

• 62—S.E. Birmingham.
• 62—N.W. Penkridge.
• 63—N.W. Market Bosworth.
• 53—N.W. Coventry.
• 54—N.W. Droitwich.
• 62—S.W. Dudley.
• 62—N.E. Lichfield.
• 63—S.W. Nuneaton.
• 54—N.E. Henley-in-Arden.

Note.—The main outlines and colors of the formations &c., in the accompanying Geological Sketch-Map correspond with those of the above mentioned one inch Survey Maps of the District.