"POSTGLACIAL FORMATIONS" OF SCOTLAND 675 



the peat and alluvia which have been referred to as underlying the 

 deposits of the 45-50 foot beach, and which, as we have seen, rest 

 upon the denuded deposits of the 100 foot beach. It is thus hardly 

 possible to escape the conclusion that the ancient land-surface buried 

 under the carse clays of the 45-50 foot beach is contemporaneous 

 with the lower forest-bed of our inland peat-mosses. This, as I 

 believe, gives us the key to the history of all the later climatic and 

 geographical changes experienced by our country. 



Summing up the evidence, we may recognize the following 

 succession of events in the history of postglacial Scotland: 



1. After the District Ice- Sheets and Mountain- Valley Glaciers 

 had disappeared, the land gained in extent — the sea eventually 

 retreating considerably beyond the present coast-line. The climate 

 at the same time gradually improved, until genial conditions super- 

 vened and a strong forest growth covered the low grounds, and 

 extended upward to elevations which trees in our country no longer 

 attain. The relics of that great forest epoch we find in the Lower 

 Forest Zone of our peat- mosses. 



2. Next followed partial subsidence of the land, accompanied 

 before long by a relapse to cold conditions. Snow-fields now reap- 

 peared, and considerable glaciers descended our mountain valleys 

 and in some places reached the sea. The climate was wet and 

 ungenial — the forests decayed, and bog-mosses gradually usurped 

 their place. To this stage we assign the Lower Peat of our inland 

 "mosses," and the 45-50 foot beach, as well as certain moraines 

 and fiuvio-glacial gravels. 



3. The succeeding stage was characterized by re-elevation of the 

 land, and the retreat of the sea beyond the present coast line. But 

 the land was probably not so extensive as during the preceding 

 forest epoch. This geographical change was marked by the disap- 

 pearance of perennial snow and ice, and by a return to dry, genial 

 conditions, apparently similar to those that formerly obtained. 

 Forests again clothed the land — flourishing in many places over the 

 surface of the now desiccated peat-mosses. This stage is represented 

 by the Upper Forest Zone of our inland peat, and by the trees which 

 occur under the deposits of the 25-30 foot beach. 



4. Once more partial subsidence ensued, and the climate again 



