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1869.] superficial deposits of Great Britain and Ireland? The fact that they are not altogether absent from Scotland and Ireland would imply 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 barrier 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 Britain 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 Ramsay 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†. In Scotland and Ireland the proofs of long- continued subaerial glaciation are most ample and abundant‡.

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 existence 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.

† Edinburgh New Phil. Journ. 1860.

‡ Geikie, Trans. Geol. Soc. Glasgow, vol. i. pl. 2.