564 



MARL LAKES. 



the surface of the earth, which had been covered for many ages, reappeared and discovered the 

 trunks of trees cut off, standing in the very sea itself, the strokes of the hatchets appearing as if only 

 made yesterday ; the soil was very black, and the wood like ebony : by a wonderful revolution, the 

 road for ships became impassable, and looked not like a shore but like a grove cut down (perhaps 

 at the time of the deluge, or not long after), but certainly in very remote times, being by degrees 

 covered and swallowed up by the violence of the seas. During the same tempest many sea-fish 

 were driven, by the violence of the waves, upon dryland." — Itinerary of Archbishop Baldwin, 1588. 

 Edition of Sir R. Colt Hoare, 1806. vol. 1. p. 217. 



However these submarine forests may be accounted for, whether by a partial subsi- 

 dence of the land, or irruption of the sea, no evidences have yet been discovered of 

 the coasts having undergone any recent movements of elevation, there being an entire 

 absence of those raised beaches full of modern sea shells, which occur around so many 

 parts of the English shores. This is the more remarkable, since Professor Sedgwick 

 and myself lately discovered examples of such elevation on the coast of North Devon, 

 opposite South Pembroke. The apparent absence of recent elevation on the shores of 

 South Wales is of high interest, in tending to strengthen the speculation which I have 

 previously entertained, concerning the ancient hydrography of Siluria, when compared 

 with that of England ; the whole region to the east, north, and south of the Severn 

 being supposed to have been elevated since the creation of existing species of mollusca, 

 whilst the country through which we have traced the range of the Silurian and other an- 

 cient rocks having been previously raised from beneath the sea, has since remained in 

 a comparatively quiescent state. 



Marl Lakes. 



An accumulation of shell marl was recently discovered ^Montgomeryshire, on an estate 

 belonging to Lord Clive. It is situated about one mile south-west of the town of Mont- 

 gomery, in a small hollow, bounded on the east by a ridge of naglike Silurian rocks, and 

 on the other sides by low hills covered with coarse gravel. This upland hollow is about 

 300 or 400 feet above the contiguous valley of the Severn. The soil being profitless 

 and wet, the farmer in occupation resolved to drain it. Beneath the surface he found 

 a bed of peat about four feet thick, and immediately under it, a stratum of fine, light 

 grey marl, filled with delicate white shells, Lymncea ovalis and other existing species. 

 When I examined the place, a deep trench several hundred feet long had been cut, and 

 the shell marl, which was about three feet thick, appeared to rest upon clay ; but as the 

 water rose to the lower edge of the marl, I could not ascertain satisfactorily the nature 

 of the sub-soil. In a moist state, this marl, though very sandy, is easily cut into 

 blocks, which, when dried, become perfectly white. 



Theoretically, the position of this shell marl is very interesting. It has been depo- 

 sited in a tract which contains no limestone, although a very minute quantity of cal- 

 careous matter is disseminated through some parts of the surrounding rocks. It is 



