676 JAMES GEIKIE 



became somewhat cold and wet. Over wide areas the forests, 

 as before, began to decay, and were eventually buried under the 

 rapidly extending peat-mosses. We cannot actually demonstrate 

 that snow-fields and glaciers reappeared at this stage. The latest 

 beach we are able to correlate with the upper peat, but that beach 

 is nowhere associated with moraines or glacial gravels. Neverthe- 

 less, we are not without evidence suggestive of the appearance at 

 this time of inconsiderable glaciers among our highest mountains. 

 The small glaciers referred to undoubtedly belong to a later date 

 than the glaciers that dropped their moraines on the 45-50 foot 

 beach. It is therefore not unreasonable to infer that our high-level 

 corrie glaciers may have been contemporaneous with the formation 

 of the 25-30 foot beach, and the Upper Peat of our inland "mosses." 

 But the chief evidence of cold, wet conditions is unquestionably 

 that furnished by the Upper Peat itself. It covers the Upper Forest 

 Zone in precisely the same way as the Lower Peat overlies the Lower 

 Forest Zone. 



5. The final stage witnessed the retreat of the sea to its present 

 le-vel. The cHmate now became drier, and peat-mosses ceased to 

 flourish as they had done in the immediately preceding epoch. Thus 

 the final phase of postglacial history may be said to be characterized 

 especially by the general decay and denudation of our peat-mosses — 

 the vegetation growing upon which is almost invariably of a drier 

 type than that found in the immediately underlying peat itself. 



Did space permit, I might follow other lines of evidence, all 

 leading to the conclusion that oscillations of climate marked the 

 closing stages of Pleistocene times. For example, the phenomena 

 presented by the alluvial terraces of our larger river valleys might 

 be referred to. It would not be hard to show that, during the so- 

 called "postglacial" period, our rivers have at some stages been 

 most active as eroding agents, while at other stages their chief work 

 has been the transportation and deposition of sediment. During 

 genial epochs, when the land stood at a higher level than now, our 

 rivers busied themselves especially in deepening and widening their 

 courses — in trying to sweep away the glacial and fluvio-glacial 

 detritus with which their valleys had been so largely choked. During 

 cold, wet epochs the land was depressed below its present level, 



