478 JReviens — Scharff's Origin of the European Fauna. 



of huge glaciers, but I am inclined to think there is equally strong 

 evidence in favour of its marine origin. Shells of Mollusca and 

 Foraminifera are very frequently present, especially in Ireland, and 

 a remarkable number of species have been identified in that country 

 by Messrs. Praeger and Wright, though the specimens, as a rule, 

 occur in a bi'oken condition. When we consider that the clay in 

 which the shells lived has probably been subjected to considerable 

 movements, it is not surprising that they should be in a frag- 

 mentary condition, and that shoi'e forms should often be found 

 mixed with those inhabiting deeper water. 



" It is probable that before the Glacial period began, a warm 

 current, not necessarily the Gulf Stream, supplied the Arctic Ocean 

 with warmth. The cessation of this current gave the first impetus 

 to the formation of ice near the North Pole, the Arctic Ocean being 

 then a closed basin. Two extensive transgressions of the Arctic 

 Ocean now took place, one inundating the plains of Arctic America 

 and the other those of Northern Russia. The latter transgression 

 covered a portion of Northern Continental Europe, and joined 

 the great inland sea, the Ponto-Caspian, by some narrow channels, 

 so that Asia became almost isolated from Europe. The Siberian 

 fauna was, therefore, unable to migrate to Europe, but a number 

 of Asiatic mammals invaded North America, which was accessible 

 by means of a land-passage across Beliring Straits. Meanwhile, 

 Arctic marine species found their way to Northern Germany, and 

 to the western portion of the newly-formed North European sea, 

 now the German Ocean. 



"The first occurrence of Arctic forms of life in the newer Tertiary 

 deposits on the east coast of England, marks therefore the period 

 when this marine transgression took place, the German Ocean 

 being at that time closed on all sides, except to the east. As 

 Arctic marine species make their first appearance in these English 

 strata in the newer Crags, the latter are synchronous with the Lower 

 Continental Boulder-clay, in which these same species are first met 

 with. This reasoning might be found fault with, but the vast 

 immigration into Europe of Siberian mammals took place after the 

 deposition of the Lower Continental Boulder-clay, during the 

 so-called Interglacial phase of the Glacial period. Now, as 

 the advance-guard of this migration reached England during 

 the time when the Forest-bed was laid down, the supposition of 

 the contemporaneousness of the newer Crags with the Lower Con- 

 tinental Boulder-clay seems to me correct. There is no reason to 

 suppose that the Interglacial era or Forest-bed period was 

 characterized by a much milder climate than that preceding it, 

 but, as it was probably much drier, the glaciers which had formed 

 on the Alps and in Scandinavia receded considerably. The 

 immediate result was a diminution in the amount of detritus cari'ied 

 to the North European sea by icebergs, so that more extensive 

 colonies of marine animals were able to establish themselves on 

 the sea-floor than during the preceding stage of the Glacial period, j 

 The narrow straits which had formed across the Tchernosjem district ■ 



