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ON THE ANCIENT GRAIIWACKE ROCKS

conspicuous on the dark rock, their state of keeping is usuallybad. Id a deserted quarry a little further on I found theSilurian forms in great abundance,—trilobites, orthoceratites,crinoidal stems, brachipods of the ancient genera orthis andatrypa, a large Maclurea, a bellerophon, casts of what seemto be turritella, a large trochus, and corals of the genus pe-traia, and of another more composite genus which was whollyunfamiliar to me, but which I find figured by Murchison asa nidulites. I found in this quarry a unique-looking uni-valve, somewhat resembling a trochus, which, if not encrustedby some mat-like coral, that has imparted to it a style of or-nament not its own, must be new; and the remains of moretrilobites, shells, and corals than I had at one time supposedall the Grauwacke deposits of the south of Scotland couldhave furnished. The place, long deserted apparently by thequarrier,—rich in mosses and herbaceous plants that lovethe shade, and shut in on every side by a thick wood,—isone in which the geologist might profitably pass many hoursin a solitude not unfavourable to thought, and rarely indeedinterrupted by the foot of man.

On ascending yet further towards the hill-top, and ex-changing for the gloom of the wood a lone and somewhatdreary heath, I found the organic remains of the rock be-coming still more numerous. Shells occur in beds and layers;and not in the rich limestone beds of Dudley have I seenthem lie more thickly. The stone here is of a firmer texturethan in the quarry, and, where unweathered, of a darker gray;and as the organisms which it incloses yield more readily onexposure than the surrounding matrix, they exist upon thesurface as mere darkened casts, but in the fresh fracture areof a pearly white. And here also trilobites and corals occuramong the shells. A little further on, the rock assumes yeta different hue : it abounds in iron, which imparts to it insome places a deep red, in others a buff-yellow hue; and the