GLACIAL GEOLOGY. 223 



marine, Iresb -water, iiiid terrestrial orgauic remains, derived undoubt- 

 edly from the so-called preglacial beds already referred to. These latter, 

 it would appear, were plowed up aud largely incorporated with the old 

 ground moraine. 



(3) The interglacial beds which next succeed contain remains of a 

 well-marked temperate fauna and flora, which point to something more 

 than a mere partial or local retreat of the inland ice. The geographi- 

 cal distribution of the beds and the presence in these of such forms as 

 JElephas antiqmis, Cervus elejjhas, C. megaceros, and a flora comparable 

 to that now existing in northern Germany, justify geologists in con- 

 cluding that the iuter-glacial epoch was one of long duration, and 

 characterized in Germany by climatic conditions apparently not less 

 temperate than those that now obtain. One of the phases of that 

 inter.glacial epoch, as we have seen, was the overflowing of the Baltic 

 provinces by the waters of the North Sea. 



(4) To this well-marked inter-glacial epoch succeeded another epoch 

 of arctic conditions, when the Scandinavian inland ice once more 

 invaded Germany, plowing through the inter-glacial deposits, and 

 working these up in its ground moraine. So far as I can learn, the 

 prevalent belief among geologists in north Germany is that there was 

 only one inter-glacial epoch ; but, as already stated, doubt has been 

 expressed whether all the facts can be thus accounted for. There must 

 always be great difficulty in the correlation of widely separated inter- 

 glacial deposits, and the time does not seem to me to have yet come 

 when we can definitely assert that all these iuter-glacial beds belong to 

 the same geological horizon. 



I have dwelt upon the recent work of geologists in the peripheral 

 areas of the drift-covered regions of northern Europe, because I think 

 the results obtained are of great interest to glacialists in this country. 

 Aud for the same reason I wish next to call attention to what has been 

 done of late years in elucidating the glacial geology of the Alpine lands 

 of central Europe, and more particularly of the low grounds that 

 stretch out from the foot of the mountains. Any observations that 

 tend to throw light upon the history of the complex drifts of our own 

 peripheral areas can not but be of service. The only question concern- 

 ing the ground moraines that has recently given rise to much discussion 

 is the origin of the materials themselves. It is obvious that there are 

 only three i)0S8ible modes in which those materials could have been 

 introduced to the ground moraine; either they consist of superficial 

 morainic debris which has found its way down to the bottom of the old 

 glaciers by crevasses ; or they may be made up of the rock rubbish, 

 shingle, gravel, etc., which doubtless strewed the valleys before these 

 were occupied by ice; or, lastly, they may have been derived in chief 

 measure from the underlying rocks themselves by the action of the ice 

 that overflowed them. The investigations of Penck, Blaas, Bohm, aud 

 Brtickner appear to me to have demonstrated that the ground moraines 



