150 A. J. Jukes-Browne — Intergkcial Land- surfaces. 



of the succeeding Newer Pleistocene epoch I quote the following : — 

 " The evidence furnished by the deposits of the two previous epochs 

 favours the assumption that, up to the close of Middle Pleistocene 

 times, the area under consideration was uninterruptedly submerged 

 to a greater or less extent . . . The deposits of the Newer 

 Pleistocene epoch now to be considered indicate the first signs 

 of subaerial erosion, and the consequent formation of river-gravel. 

 . . . During this stage the rivers cut down their valleys through 

 the older Boulder-clays and sands to within about twenty feet 

 of their present depths, and left their gravels stranded as terraces at 

 various heights above their present courses. Upon these inter-glacial 

 gravels, or upon the older rocks, there frequently rests a Boulder- 

 clay sometimes reaching a considerable thickness." ^ This later 

 Boulder-clay would appear to be contemporaneous with the marine 

 clays of Staffordshire and Cheshire on the one hand and of Lincoln- 

 shire on the other, though this point cannot be taken as proved. 



Lastly, with regard to the Pleistocene succession in North Wales, 

 we have the concurrent testimony of Mr. Mellard Eeade, Mr. A. 

 Strahan, and Dr. Hicks. Mr. Strahan sums up as follows : ^ — 

 " While, however, there is a general agreement as to the marine 

 origin of the sand, gravel and associated Boulder-Clays, there is an 

 equally wide-spread opinion that the tough and very strong base- 

 ment-clay seen at Colwyn Bay, Bryn Elwy, Llanefydd and other 

 places in North Wales is the product of an ice- sheet." The dis- 

 tinction between the older and newer Boulder-clays seems therefore 

 to be as marked in North Wales as it is in Lincolnshire ; and if 

 Dr. Hicks's views with regard to the relation of the caves to the 

 newer glacial deposits are confirmed, the Pleistocene record in North 

 Wales may be read thus : — 



(1) Intense glacial conditions; Wales buried in ice, but the relative 



level of land and sea not yet known. 



(2) Eetreat of the ice, exposal of land-surface, and occupation 



of the district by Man and the newer Pleistocene Animals. 



(3) Extensive submergence, during which the later (marine) 



Glacial beds were deposited. 



(4) Elevation and re-occupation of the country by man and animals. 

 All recent observations tend to show the high probability of 



there having been a free land-surface over the greater part of 

 England in the midst of what is usually called the Glacial period. 

 During this Inter-Glacial period valleys were excavated, caves were 

 formed, and a long process of subaerial detrition went on ; the caves 

 being occupied by Hyenas, while the plains were inhabited by an 

 assemblage of animals very little different from that which again 

 occupied the country after the second Glacial episode had passed away. 

 At present this is little more than a theory, but it will be interest- 

 ing to see how far future investigations will confirm what I have 

 suggested, and some geologists may perhaps be stimulated to search 

 for further evidence bearing upon the question. 



1 Quart. Journ. Geol. Soc. vol. xlii. p. 466. ^ q_ j_ g. S. vol. xlii. p. 386. 



