1869.] DAWKINS BEITISH POSTGLACIAL MAMMALS. 209 



superficial deposits of Great Britain and Ireland? The fact that 

 they are not altogether ahsent from Scotland and Ireland would im- 

 ply that those two countries were not insulated from the mainland 

 of Europe during the whole of the Postglacial epoch. And yet 

 there must have been some harrier to prevent their immigration. 

 It is undoubtedly true that since Scotland was submerged to a depth 

 of 2000 feet (deeper than any other part of Britain has yet been 

 proved to have been submerged), the Scotch lowlands would emerge 

 from the waves of the glacial sea long after middle and south Bri- 

 tain had been occupied by the Postglacial mammals, if the rate of 

 elevation were equal over the whole British area ; their remains, 

 therefore, might be expected to be more rarely met with in Scotland 

 than in England. Sir Charles Lyell* accounts in this manner for the 

 rarity of Postglacial mammals in Ireland. But while this may be 

 one of the causes, ii seems to be only secondary and subordinate to 

 another which as yet has not been explained. A map on which I 

 have laid down the distribution of the Postglacial mammals in the 

 United Kingdom (and which any one can construct for himself by 

 using the Table of distribution) shows large areas in which I have 

 no evidence that Postglacial Mammalia have as yet been discovered. 

 A line drawn from St. David's Head due east as far as Hereford, 

 and thence passing northwards through Shrewsbury, and sweeping 

 round in a westerly direction through St. Asaph as far as Holyhead, 

 circumscribes with the sea-board a region which is singularly devoid 

 of Postglacial mammals, but which has been proved by Professor 

 Bamsay to be full of traces of terrestrial glacial action. Again, a 

 line drawn from the mouth of the Ribble to that of the Tees is the 

 southern boundary of the barren area of Cumberland, Westmoreland, 

 North Lancashire and Northumberland, in which Mr. Hull has met 

 with unequivocal traces of the former existence of glaciers f. In 

 Scotland and Ireland the proofs of long- continued subaerial giaci- 

 ation are most ample and abundant J. 



These areas therefore agree, not only in the rarity or absence of 

 the fossil mammals, but also in presenting traces of the action of 

 land-ice. If the two phenomena be coupled together we have in 

 my opinion a vera causa. If we suppose that the ice-sheet, the 

 work of which looks so fresh and recent in these areas, was in ex- 

 istence while the Postglacial mammals were dwelling in Britain, 

 their scarcity or absence must of necessity follow. In Scotland, the 

 fact that in two cases the Mammoth has been found underneath, 

 and in one case in the midst of the till, implies that in that country 

 glacial phenomena were going on while Postglacial mammals were 

 living in the neighbourhood. Both Mr. A. Geikie and Sir Charles 

 Lyell agree in the belief that the glaciers had not forsaken the Scotch 

 highlands in the days when man dwelt on the banks of the Somme 

 and in the valley of the Thames. On the whole, therefore, it may 

 be assumed, with a very high degree of probability, that the higher 

 grounds of North Wales and of the barren areas in England and 



* Antiquity of Man. t Edinburgh New Phil. Journ. 1860. 



X Geikie, Trans. Geol. See. Glasgow, vol. i. pi. 2. 



