382 Mr Smith on the Changes of the Level of the Sea, 



by Dr Scouler of the Royal Society of Dublin, and Dr Cowper 

 of the University of Glasgow, who visited these localities, thai, 

 in both instances, they were embedded in the till. At Kilmaurs 

 they were associated with sea-shells ; and, on one occasion, I 

 also found shells embedded in it, much broken, and deprived of 

 their colour. Mr Trimmer, in describing the diluvial deposits 

 in Caernarvonshire, in the proceedings of the Geological So- 

 ciety,* states that he found broken shells in the diluvium of 

 the low cliff near Beaumaris. He also found broken shells in 

 a bed of sand, on the summit of Moel Tryfane, 1400 feet above 

 the level of the sea. The expression seems to imply alluvial 

 rather than diluvial agency. Mr Trimmer, however, informs 

 me that he ascribes their presence at so high an elevation to 

 the latter cause, the beds having all the appearance of violent 

 action, and the subjacent rocks worn and scratched by friction 

 of transported pebbles. Mr Phillips also is inclined to tliink 

 that in Holderness the irregularity of deposition of the shelly 

 gravel seems to point to diluvial currents rather than to change 

 of level, t 



It is not, therefore, a necessary inference that the mere dis- 

 covery of sea-shells at high levels is a proof of permanent sub- 

 mergence. Their fragments, like those of coal, sandstone, and 

 shale, mark that the distance from which they have been trans- 

 ported is a short one. It is only when found in situ in regu- 

 larly stratified beds that we are entitled to draw such conclu- 

 sions; but their presence in diluvial beds must be held as an 

 exception to the general rule. 



Although this is not the place to offer any speculation re- 

 specting the origin of the till, I think it evident that it must 

 have arisen from causes altogether different from those which 

 have produced the marine alluvia. Whatever they were, they 

 must have been violent and transitory. Of their violence we 

 have ample proof in the size of the fragments they have trans- 

 ported, as well as the erosion of the rocks over which they 

 have passed, but that they suddenly ceased must be inferred 

 from the confused manner in which the different parts of the 

 till are arranged. Submarine currents might indeed have moved 



>' ' — 



* Vol. i. p. 332. t Treatise on Geology, p. 198. 



