234 PE0FESS0E JAMES GEIKIE, LL.D., D.C.L., F.E.S., ETC., ON 



therefore, that we derive our fullest knowledge of the life of 

 the period. But a comparison of their organic remains with 

 those that occur in the glacial and interglacial deposits of 

 alpine and northern lands shows us that the Pleistocene 

 accumulations of glacial and extra-glacial countries are con- 

 temporaneous — for there is not a single life-form obtained 

 from interglacial beds which does not also occur in the 

 deposits of extra-glacial regions. The converse is not true — 

 nor is that to be wondered at, for interglacial deposits have 

 only been sparingly preserved. In regions liable to glaciation 

 such superficial accumulations must frequently have been 

 ploughed up and incorporated with groundmoraine. It was 

 only in the extra-glacial tracts that alluvia of interglacial age 

 were at all likely to be preserved in any abundance. To fully 

 appreciate the climatic conditions of the Pleistocene period, 

 therefore, it is necessary to combine the evidence derived 

 from the glaciated areas with that obtained from the lands 

 that lay beyond the reach of the ice-plough. The one is the 

 complement of the other, and this being so, it is obvious that 

 any attempted explanation of the origin of the glacial period 

 which does not fully realise the importance of the interglacial 

 phase of that period cannot be accepted. 



But if the climatic changes of Pleistocene times are the 

 most important phenomena which the geologist, who essays to 

 trace the history of that period is called upon to consider, he 

 cannot ignore the evidence of contemporaneous geographical 

 mutations. These are so generally admitted, however, that 

 it is only necessary here to state the well-known fact that 

 everywhere throughout the maritime tracts of the glaciated 

 lands of Europe and North America, frequent changes in the 

 relative level of land and sea took place during Pleistocene 

 and postglacial times. 



I must now very briefly review the evidence bearing on 

 the climatic conditions of postglacial times. And first, let 

 it be noted that the closing stage of the Pleistocene period 

 was one of cold conditions, accompanied in North-Western 

 Europe by partial depression of the land below its present 

 level. This is shown by the late-glacial marine deposits of 

 Central Scotland and the coast-lands of Scandinavia. The 

 historical records of the succeeding postglacial period are 

 furnished chiefly by raised beaches, river- and lake-alluvia, 

 calcareous tufas, and peat-bogs. An examination of these 

 has shown that the climate, at first cold, gradually became 

 less ungenial, so that the Arctic-alpine flora and northern 



