Having referred in the last section to brick-making, lime, cement, and Totternhoe stone, very little remains for mention in the present one; as the absence of mines is one of the features of Hertfordshire and the adjacent counties.

Reference may, however, again be made to the so-called coprolite beds of the chalk-marl which were worked in the neighbourhood of Hitchin in the early part of the first half of last century as a source of phosphoric acid for agricultural manure. The irregularly shaped black nodules of phosphate of lime occur crowded together in a comparatively thin bed. They were dug out, and washed from the marl in which they were embedded on the spot in large circular tanks through which a wheel was made to revolve by horse-labour; and then carted away to be converted by a chemical process into superphosphate. After the excavation of the coprolite bed from one strip of a field, the marl from the next was thrown in, and the top soil replaced, so that the land was left in as good, or even better, condition than previously. The industry was continued till all the beds situated at or above a level which it paid to work were exhausted.

In winter there is a considerable local trade in gravel and shingle, dug mainly in the valleys. Twenty years ago this trade was much more extensive in some districts than is at present the case; this being due partly to the exhaustion of the deposits, partly to the fact that in districts served by the Midland Railway the use of syenite from Mount Sorrel and Charnwood Forest, in Leicestershire, has to a considerable extent replaced flint-gravel as road-metal on the main highways of the county and in the metropolitan districts. Formerly, very large quantities of gravel were sent from St Albans and Harpenden to the northern metropolitan suburbs such as Hendon and Child’s Hill; but most of that now dug is employed for road-metal on the local by-roads. Here it should be mentioned that in Hertfordshire phraseology the term “gravel” is used exclusively to denote the coarse big-stoned material used as road-metal; what is ordinarily denoted as “gravel”—that is to say the material employed for garden-paths—being locally known as “hoggin.” Flints picked from the fields of the chalk area have a higher value as road-metal than dug gravel, owing to their superior hardness; the so-called “quarry-water,” which is present in all dug gravel, having been long since dried out.

“Facing” flints for building purposes is an art much less commonly practised in the county than was the case in earlier days; and when buildings of faced flint are contemplated it is generally necessary to send to a distance in order to secure the services of an expert in the facing process.