Ancient Landscapes of the Grand Canyon Region / The Geology of Grand Canyon, Zion, Bryce, Petrified Forest & Painted Desert

CHAPTER III THE PALEOZOIC ERA

It was during the third or middle chapter in the earth’s history that all of the apparently horizontal, upper layers in the Grand Canyon walls were formed. As will be seen in the succeeding pages, some of these rocks are sandstones formed from the sands of early beaches or sand dune areas, others are shales—the hardened muds of ancient river deltas—and still others are limestones built up by accumulations of plant and animal remains on sea bottoms. All are rocks formed by the deposition of sediments by wind and water during vast intervals of time. In them have been hidden and preserved many forms of life. Seashells, footprints, fern impressions, and various other traces of early plants and animals remain to tell the story of these ancient times. It is of special interest to note that in rocks formed during the earliest part of this chapter are found the first definite traces of animal life, that in other rocks of this chapter have been found evidences of primitive fish, and that in the most recent rocks of this group occur the traces of early reptiles, insects, ferns, and cone-bearing plants. In the walls of Grand Canyon examples of all of these fossils have been found, and these will be described in detail in the succeeding pages.

FIRST ANIMAL LIFE—THE TONTO ROCKS
(CAMBRIAN PERIOD)

Great highlands which were formed in the Grand Canyon region during the Second Era of history were afterwards gradually worn away by erosion until near the start of the next era a flat, almost featureless plain existed. Here and there, however, isolated hills of dark, crystalline rocks of the First Era stood above the general surface, as seen opposite Yaki point. In other places, such as to the west of where Bright Angel Creek now flows, small mountains of red Algonkian rocks (Second Era) remained. Around and against these, sediments were then deposited. Pebbles and sands accumulated, forming a thick layer which today appears as the brown sandstone rim of the Inner Gorge. These represent the first deposits of the Third Era. But the sea was encroaching upon the land during this period, and gradually the sand deposited near shore was covered by mud and this in turn by lime far out from the beach. Today this series of sand, mud and lime is found represented in the rocks of the Tonto Platform in Grand Canyon.

SCENE ON CAMBRIAN SEA FLOOR IN GRAND CANYON REGION (RECONSTRUCTION. MUSEUM NORTHERN ARIZONA)

Along the Tonto Trail a few hundred yards east of Indian Gardens numerous primitive sea animals have been found buried and preserved in layers of thin shale. Many of these are creatures with rounded shells smaller than the nail of a person’s little finger, others are animals related to the snail, and still others are crab-like creatures known as trilobites. The trilobites undoubtedly were the rulers of that age for they excelled not only in numbers but in size. Some specimens from Grand Canyon have measured over three inches in length. Despite this size, however, the trilobites and their associates from the Tonto Platform represent some of the earliest known forms of animal life.

TRILOBITES PRESERVED IN GREEN SHALE OF GRAND CANYON WALLS (ONE-EIGHTH NATURAL SIZE)

THE MISSING PERIODS OF THE THIRD ERA
(ORDOVICIAN AND SILURIAN PERIODS)

The geologist has found that two long periods of history are lacking in the great succession of ages represented by the strata in the Grand Canyon walls. These missing periods which belong to the Third Era are known as the Ordovician, the time when fish first appeared in the seas, and the Silurian, the time when millipeds and scorpions became our first air breathers. These ages immediately followed the Cambrian and involved millions of years. The absence of the first of them is explained by some geologists as the result of its rocks having been completely worn away at a later time. It seems more probable, however, that the Grand Canyon region was above sea level during these two ages so that no sediments were accumulated and consequently no rocks formed.

THE AGE OF FISH
(DEVONIAN PERIOD)

A FRESH WATER FISH OF DEVONIAN AGE

During that period of geologic time commonly known as the “age of fish,” sands and limes were accumulated on the surface of the Grand Canyon region filling in old river channels and burying the bodies of fish and other animals. The deposits formed at this time were later eroded to a large extent. The surface of the land was worn and washed away until finally only isolated patches or pockets of limestone and sandstone remained. These we find today exposed in the walls of the Grand Canyon occurring just at the base of the great Redwall cliff in about fifteen different localities.

Although fish were rulers of the age during Devonian times, they were of primitive types and apparently depended for defense upon bony skin armour rather than upon speed. The plates and scales of fresh-water fish have been found preserved in the lavender rocks of this age in the Grand Canyon.

SEA LIFE FROM THE NORTH—THE REDWALL LIMESTONE
(MISSISSIPPIAN OR LOWER CARBONIFEROUS PERIOD)

REDWALL FOSSILS (NATURAL SIZE)

One of the most prominent and conspicuous features of the Grand Canyon is the great red cliff of limestone about midway in its walls. This cliff is the highest in the Canyon—averaging about 550 feet in the area of Bright Angel Canyon. In most places it is almost vertical, and in some it even overhangs to such an extent that a visitor once aptly said, “The Washington Monument might be placed beneath it and kept out of the rain.”

To the prospector this formation is known as the Blue Lime; to the geologist it is the Redwall Limestone. Both are correct. Actually the rock is a rather pure limestone of a grey or bluish color, but in most places where seen, its surface has been stained a bright red by iron oxides from above. It appears throughout the Grand Canyon as a wide band or ribbon of red.

HAVASU FALLS IN REDWALL LIMESTONE. GRAND CANYON

Large amphitheaters, many curving alcoves, caves, and solution tunnels are all characteristic features of the great Redwall. It is composed of relatively pure lime so rain and other waters have a chemical action upon it—they leach and dissolve it. Waters all tend to drain toward curving centers, and so increase this curving. Everywhere the rounding off of corners takes place.

The origin of the Redwall Limestone is as interesting as its form. The purity of the lime indicates that it was built up in a relatively wide and quiet sea. Its composition represents a vast accumulation of the skeletons of ancient plants and animals. Seashells are found in great numbers, some of them preserved in delicate detail. These and other forms of ocean life clearly indicate that a great sea connection then existed between this region and that of western Canada to the north.

TRACKS IN THE SUPAI SANDSTONE
(PERMIAN PERIOD)

During that period in geological history known as the Permian, when some of the beds of soft coal in eastern America were being formed, a large area in northern Arizona was receiving red sediments from the east, probably carried by rivers from the granitic highlands of that region. Today these sediments appear in the Grand Canyon walls as alternating layers of red sandstone and shale immediately above the great Redwall. They are almost a thousand feet in thickness.

TRACKS OF SHORT-LEGGED PREHISTORIC ANIMAL. SUPAI FORMATION. GRAND CANYON

When the red beds were accumulating in this region, the climate probably was more or less arid; the vegetation consisted principally of ferns and other lowly plants; and the animal life included a group of large but primitive four-footed creatures. Numerous tracks of the latter, preserved in the walls of Grand Canyon, have provided one of the most interesting discoveries of recent years. Some of these footprints are several inches in length, and the number of toes varies between three and five. They show no close relationship to the tracks of other localities, and apparently represent a fauna new to North America.

LANDSCAPES OF THE HERMIT SHALE
(PERMIAN PERIOD)

LANDSCAPE AT TIME HERMIT SHALE WAS FORMING (RECONSTRUCTION. MUSEUM NORTHERN ARIZONA)

FOSSIL FERN FROM THE HERMIT SHALE (REDUCED)

Concerning the conditions under which the topmost red formation of the Grand Canyon (the Hermit Shale) was developed, and the nature of its origin, we have today a rather definite and interesting picture. A wealth of fossil plants and a number of tracks of animals have been found excellently preserved in its muddy layers, and by means of these and other indications the following conclusions have been drawn.

The Hermit Shale represents accumulations of mud and fine sandy material deposited probably by streams flowing from the northeast. Here and there are found evidences of pools and arroyos with wavy ripple marks on their borders and a thin film of shiny slime covering the surface. The trails of worms, the footprints of small salamander-like animals, and the fronds of ferns, mostly mascerated or wilted, are found delicately preserved in this slime. Raindrop impressions, the molds of salt crystals and numerous sun-cracks also add to the picture. This region has been described by Dr. David White as “the scene of showers, burning sun, hailstorms, occasional torrents and periods of drought and drying up of pools” during Hermit times.

Thirty-five species of plants are at present known from the Hermit Shale of Grand Canyon. Many of these have not been found elsewhere in the world, though some were representatives of European plants, and others had their closest relations in central Asia, India, Australia, Africa, and South America. This fossil flora consists principally of ferns and small cone-bearing plants, all of which were relatively dwarfed in size and appear less dense than those of corresponding age found in eastern America. They apparently indicate a semi-arid climate with long dry seasons, for the absence of moist-climate and swamp-loving types is noticeable.

Several insect wings have been found in the Hermit Shale, one of which was four inches in length. Numerous footprints of vertebrate animals have also been found, and undoubtedly represent an interesting fauna.

WIND-BLOWN SAND—THE COCONINO
(PERMIAN PERIOD)

The light-colored formation which appears as a conspicuous ribbon-like band around the upper part of the Grand Canyon has long presented a puzzle concerning its origin. The grains of white sand of which it is composed apparently were deposited at steep angles, for the many and varied slopes which were formed may be readily seen today on the surface of the rock. These slopes were probably once the lee sides of sand dunes deposited by winds in an area bordering the sea. We find the only traces of life in this formation represented by the trails of ancient worms and insects, and by the foot-prints of early lizard, or salamander-like creatures. Already the tracks of some 27 species of animals have been discovered in this sandstone within the Grand Canyon, though strangely enough no bones have yet been located.

WIND-BLOWN SAND. COCONINO FORMATION. GRAND CANYON

TRACKS OF PRIMITIVE FOUR-FOOTED ANIMALS, COCONINO SANDSTONE. GRAND CANYON PHOTO BY E. W. ENSOR

WARM SEAS FROM THE WEST—THE TOROWEAP AND KAIBAB FORMATIONS
(PERMIAN PERIOD)

SEASHELLS FROM KAIBAB LIMESTONE (REDUCED)

Along both sides of Grand Canyon at the top, two buff and gray layers of limestone stand out as massive cliffs separated by a tree-covered slope. The upper of these limestones forms the plateau surface and may be seen for a great distance in every direction. Both layers were formed as the result of vast accumulations of organic and sandy materials on sea bottoms, and in places are composed largely of the remains of marine life—shells, corals and sponges. The teeth of sharks have also been found in the upper limestone.

SEA LILY OR CRINOID (REDUCED)

HORN CORAL (NATURAL SIZE)

During the early stages of the period when these marine animals lived and multiplied in the region, a great body of salt water extended over its surface from far to the west, remained briefly, then retreated from the area. Soon, however, marine waters advanced once more and another sea was formed with its shoreline extending eastward even beyond the region in which we now find Grand Canyon. Evidences of the second and larger sea are found beyond Flagstaff to the south, in the Painted Desert to the east, and almost to Zion Canyon to the north.

The presence of corals and sharks’ teeth not only indicates that this region was covered on more than one occasion by marine waters, but also suggests that these seas were warm and shallow. This is estimated to have been some 200 million years ago.

FOSSIL SHARK’S TOOTH (NATURAL SIZE)

ROCKS OF THE FOURTH ERA
The Painted Desert and Zion Canyon Region

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FIRST ANIMAL LIFE—THE TONTO ROCKS (CAMBRIAN PERIOD)

THE MISSING PERIODS OF THE THIRD ERA (ORDOVICIAN AND SILURIAN PERIODS)

THE AGE OF FISH (DEVONIAN PERIOD)

SEA LIFE FROM THE NORTH—THE REDWALL LIMESTONE (MISSISSIPPIAN OR LOWER CARBONIFEROUS PERIOD)

TRACKS IN THE SUPAI SANDSTONE (PERMIAN PERIOD)

LANDSCAPES OF THE HERMIT SHALE (PERMIAN PERIOD)

WIND-BLOWN SAND—THE COCONINO (PERMIAN PERIOD)

WARM SEAS FROM THE WEST—THE TOROWEAP AND KAIBAB FORMATIONS (PERMIAN PERIOD)