84 NEOZOIC TIME. [CHAP. XIII. 



mined, though I have elsewhere recorded facts which seem 

 to favour the latter supposition. 1 



I would here remark that though Professor J. Geikie 

 admits the occurrence of a great submergence by which 

 England, Wales, and Ireland were depressed to at least 

 1,500, and probably to 2,000 feet below the sea-level, yet 

 the deposits which he would refer to the epoch of this 

 grand subsidence are few and physically unimportant. He 

 excludes every Boulder-clay from the category of marine 

 deposits, and explains the absence of thicker and more 

 extensive records of this important episode by the hypo- 

 thesis that they were swept out and worked up into the 

 Boulder- clays formed by a second great ice -sheet after the 

 country emerged from the sea. He is therefore under the 

 necessity of supposing that the second ice-sheet was nearly 

 as extensive and as massive as the first, a result which he 

 himself appears to consider surprising, as it certainly is. 

 If, however, we admit that the later Boulder-clays were 

 formed during the submergence and on the sea-floor, no 

 such necessity arises, and we possess in them, and the 

 shelly sands associated with them, a set of deposits which 

 is more proportionate to the magnitude of the subsidence 

 and the time it must have occupied. 



It is remarkable that no Drift with marine shells has 

 been found at similar high levels in Scotland, a fact which 

 seems explicable only on the supposition that the conditions 

 in England and Scotland were essentially different, and 

 that the mass of ice which had previously accumulated 

 over Scotland was so thick as to keep out the sea-water 

 and to prevent its ever rising much above the contour of 

 600 feet. Professor G-eikie himself estimates the thickness 

 of the Scotch ice at more than 2,000 feet, and observes that 

 " to cause such a mass to float, the sea around Scotland 



1 "Quart. Journ. Geol. Soc.," vol. xli. p. 128, and "Geol. Mag.," 

 1887, p. 147. 



