Zoophyta Syringopora reticulata, Turbinolia fungites, Lithostrotion irregulare.
Echinodermata
„
„
„ 		Actinoerinus aculeatus, et
lævissimus, Platyerinus lævis et rugosus.
Poteriocrinus crassus, et pentagonus.
Rhodocrinus costatus, et granulatus.
Mollusca Dimyaria. Pallastra complanata.
Brachiopoda.
„
„
„
„ 		Terebratula hastata.
Spirifer glaber, et rhomboideus.
Chonetes cornoides, et papilionacea.
Leptœna analoga.
Productus cora, et longispinus, et martini, et pustulosus et cornoides.
Lamellibranchiata. Monomyaria.
Aviculopecten fallax.
Dimyaria.
Psammobia complanata.

Pisces.

Ctenacanthus tenuistriatus.
Cladodus conicus.
Psammodus porosus, et rugosus.

The millstone grit beds immediately succeed those of the carboniferous limestone just described, forming a similar belt round the Forest, and disappearing with it on the Blakeney side of the basin. Its chief interest consists in the circumstance that it has been employed from very early times as a material for building; for though it contains a vein of iron ore, little has been done in mining it. Most of the old buildings adjoining the parts where this grit crops out are formed of it, as several of the ancient neighbouring churches show, and likewise the oldest lodges in the Forest; now, however, this kind of stone is seldom used except for boundary walls, and such kind of rough work.

The rest of the outer circle of high land, on whose summit the observer has been supposed to be standing, and which so definitely marks the Forest coal-field, comprises the lower coal measures, containing the lower and upper Trenchard veins, the Coleford High Delf, with the Whittington and Nag’s Head seams, which together give about eleven feet of coal. Of these the Coleford High Delf, averaging a thickness of upwards of five feet, and extending over an area of 16,000 acres, is undoubtedly the chief, although in some places it has suffered from various disturbances, the principal of which occur in the neighbourhood of Coleford, extending in a line from Worcester Lodge to Berry Hill, and is marked on the surface by a succession of pools, named Howler’s Well, Leech Pool, Crabtree Pool, Hooper’s Pool, and Hall’s Pool. Mr. Buddle describes the width as varying from 170 to 340 yards in the most defined part, called by the colliers the “Horse,” and the dislocations adjoining, the “Lows.” “It is not,” he remarks, “what geologists term a fault, as there is no accompanying dislocation of the adjoining strata. In its underground character it is similar to those washes or aqueous deposits in many coal districts, but it differs from them in not being under the bed of any river, nor in the bottom of a valley, nor does it show itself at the surface.” And he adds, “On considering the various phænomena presented by this fault, and the seam of coal on each side of it, we may infer that it occupies the site of a lake which existed at the period of the deposition of the High Delf seam, and that

the carbonaceous matter which formed the seam was accumulated while the water was deep and tranquil. On the water being discharged from the lake, the ‘Horse’ itself occupied the bed of the river, by which the complete drainage of the lake was effected, and which washed the coal entirely out.”

The same scientific observer records an extraordinary depression about half a mile to the south-east, in the direction of the “Horse,” and in the same seam of coal, amounting to about twenty feet in depth, and of an oval shape. Various other defects and disturbances in the Coleford High Delf are detected from time to time by the new workings, especially in those places where the surface is most uneven. Thus its outcrop at Lydney is very imperfectly defined, and at Oakwood Mill the vein is rendered worthless by a fault, whilst on each side of the Lydbrook valley there is a contortion, by which it is thrown down in one instance seventy yards, and in two others thirty yards each.

Such is the geological character of the conspicuous range of hills by which the Dean Forest coal-field is bounded, especially on its north and east sides. The following table gives their height in feet at certain places above the sea:—