ScHARFF — On the Origin of the European Fauna. 495 



liighway for the migration of tlie Arctic animals and plants. "When the 

 lowlands of Ireland were covered by the sea, which event I presume 

 happened some time during the Glacial Period, a broad belt of land 

 probably remained separating the Atlantic from this westward 

 extension of the Irish Sea. 



The boulder-clay which covers such vast tracts of country in 

 the British Islands and the Continent is now generally believed to 

 be the ground moraine of huge glaciers, but I am inclined to think 

 there is equally strong evidence in favonr of its marine origin. 

 Shells of Mollusca and Eoraminifera are very frequently present, 

 especially in Ireland, and a remarkable number of species have been 

 identified in that country by Messrs, Praeger and Wright (80), 

 though the specimens as a rule occur in a broken 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 fragmentary condition and that shore 

 forms should be often found mixed with those inhabiting deeper 

 water. 



Before concluding these notes on the Glacial Period, I will give 

 a short sketch of what I think may have been the course of events 

 during that time. 



It is probable that before the Glacial Period began, a warm current, 

 not necessarily theGulf Stream, supplied the Arctic Ocean with warmth . 

 The cessation of this current gave the first impetus to the formation 

 of ice near the IS'orth 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 jSTorthern 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 

 Behring Straits. Meanwhile, Arctic marine species found tlieir 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 Englisli strata in the newer 



