Essay on Geology. 95 



in great quantity near Bitton. The variegated character which gives name 

 to the poecilite, is well exhibited in the uew cut of the river at Bristol, 

 which is excavated in this rock. 



The next deposit of Lias, an argillaceous limestone, which rests on the 

 poecilite, spreads over the whole of the lower, but still somewhat elevated 

 platform which forms the base of Dundry Hill j and occupies all the 

 grounds of middle elevation from hence to Bath, the valleys being oc- 

 casionally excavated into the subjacent poecilite, and the hills formed by 

 the superincumbent oolite. The organic remains of the lias are very 

 abundant and interesting ; and we shall be struck by trampling, at every 

 step, on its ammonites, gryphites, and plagiostomae. A very perfect 

 skeleton of the plesiosaurus has been found at Bitton. We need not here 

 repeat what we have said in the introductory notice of the last number, with 

 respect to the distinction between the older order of organic remains of 

 the carboniferous limestone, &c., and the secondary fossils of the lias and 

 oolites ; but our walk up to Dundry may afford us an opportunity of illus- 

 trating this in a very striking manner. When, from the pcecilite of the 

 valley, we first ascend the lias platform, a little beyond Bedminster, we 

 are only separated by the narrow valley of the Ashton brook, from the 

 carboniferous lime of Leigh Down, If we cross this valley for a few 

 minutes, we shall find the carboniferous lime, often a mere aggregate of 

 thousands of encrinites, madrepores, and jieculiar shells ; and on the lias 

 platform, on the other side this narrow valley, we shall find an equal 

 abundance of pentacriuites, gryphites, ammonites, and other shells ; but 

 we shall in no instance find a single species common to the two rocks, 

 though here scarcely half a mile apart. This shews us, that geographical 

 proximity can have nothing to do with the orderly distribution of organic 

 remains ; and we shall be impressed with the truth of the depcndance of 

 this order of distribution, on the geological succession of beds, if we com- 

 pare our two parcels of carboniferous limestone and lias fossils, with others 

 from the most remote localities. The former, if compared with collections 

 from Derbyshire, Kilkenny, or the banks of the Meuse, will be found 

 identical ; as will the latter, if placed by the side of specimens from Lyme 

 Regis in Dorsetshire, the lowest beds of the Whitby coast in Yorkshire, 

 from Boll in Wurtcmberg, from many parts of the Jura chain, &c. 



The deposit next succeeding to the lias, is that of the calcareous free- 

 stone, called oolite, or roe stone, from its granular concretionary texture 

 somewhat resembling the roes of female fishes. These deposits constitute 

 the mass of a long range of hills, stretching across the island from York- 

 shire on tiic N. E., to Dorset on the S. W. From Dundry we may observe 

 a long chain of this range, here called the Cottcswolds, stretching away 

 from Fromc, on the south by Bath, towards the neighbourhood of Gloucester 

 and Chippenham, on the north. This chain presents a steep escarj)ment 

 towards the west ; it often approaches, and sometimes exceeds, a thousand 



