504 Proceedings of the Royal Irish Academy. 



of the Glacial Period, the fauna is supposed to have very gradualljr 

 retreated from these high northern latitudes, "which are no"w almost, 

 uninhabitable, 

 p. 4-51 Against these views it has been urged that, to some extent, the 

 Mammalian bones and carcases found in the K'ew Siberian Islands, rest 

 on a solid layer of ice, and that as this ice was probably formed during 

 the Glacial Period, the migrations must have taken place in post-Glacial 

 times. This presupposes an extraordinary amelioration of climate 

 in Siberia, the effects of which certainly would have been felt in 

 Europe, but of which we have no evidence, 

 p. 452 There is geological evidence that a marine transgression took place- 

 in Northern Russia in early Pleistocene times, and that at the same 

 time the united waters of the Caspian Sea and the Sea of Aral covered 

 a large tract of the central parts of that country. It is supposed by 

 some naturalists fand in favour of this view I have collected some 

 additional facts) that the "White Sea and this large inland sea were 

 connected right across Kussia, thus forming a barrier by means of 

 which the Siberian fauna was prevented from migrating to Europe. 

 It is also suggested that the whole of the Continental boulder-clay is a 

 marine deposit, and that its maximum southward extension approxi- 

 mately marks the shores of a Xorth European Ocean, 

 p. 4C.5 In support of this view are quoted a number of Caspian species 

 which must have come from the Arctic Ocean, and the fact of the 

 occurrence of Dret/sseymia pohjmorpha, in the lower and not in the upper 

 Continental boulder-clay, thus proving that a migration took place in 

 both directions. 

 p. 466 As all the deposits in Continental Europe, containing remains of 

 Siberian Mammals, are of a later age than the lower boulder-clay, 

 it seemed to me that the connexion between the Aralo-Caspian 

 and the ^hite Sea must have ceased to exist during and after the 

 Interglacial phase of the Glacial Period, which would also explain 

 the absence of Dreyssensia in the more recent beds. The Siberian 

 fauna probably began to pour into Europe immediately after the 

 deposition of the lower Continental boulder-clay. But since the first 

 Siberian Mammals made their appearance in England, during the 

 deposition of the Forest-bed, the British newer Pliocene beds must be 

 contemporaneous with this boulder-clay. Further proof of this will 

 be mentioned later on. 

 p. 46S Some further evidence is now given in favour of the marine origin 

 of the boulder-clay, and the causes of the absence of marine shells in the 

 Russian deposits are explained. 



