''POSTGLACIAL FORMATIONS" OF SCOTLAND 68i 



is nearly always of a drier type than that occurring at slightly greater 

 depths — a fact, he remarks, not without its bearing upon the present 

 denuded state of the "mosses." 



From this brief and imperfect summary of the results obtained 

 by Mr. Lewis, it will be admitted that the geological evidence of 

 climatic changes in so-called postglacial times has been decidedly 

 strengthened. It is most satisfactory to learn that a definite zone 

 of arctic plants is intercalated in the peat separating the lower from 

 the upper forest-bed. The occurrence of these plants midway 

 between the two forest zones, and the succession of plant remains 

 in the peat-beds immediately overlying and underlying the zone of 

 arctic plants, all point to a gradual change from dry forest to wet 

 moorland, and from wet moorland to cold tundra, and again from 

 cold tundra to wet moorland, and from the latter to dry forest. 



In the peat overlying the Upper Forest zone no trace of arctic 

 plants has been met with. Mr. Lewis thinks it is possible, however, 

 that these may yet be detected in those high-level peat-mosses which 

 were formed contemporaneously with the moraines of the youngest 

 corrie glaciers. It may be so; but I doubt whether the wet and 

 relatively cold conditions indicated by the high-level corrie moraines, 

 and the peat which covers the Upper Forest zone, were sufiiciently 

 pronounced to induce any conspicuous modification of the flora. 

 All we can infer is that the climate was inclement enough to check 

 forest growth, and to favor the increase of the bog-moss and its 

 allies. The temperature, however, need not have differed greatly 

 from the present. Only a slight lowering of the present tempera- 

 ture, with a corresponding small increase of precipitation, would cover 

 our highest mountains with perennial snow- caps and reproduce their 

 corrie glaciers. 



The various superficial accumulations which have formed the 

 subject of this address are usually classified as postglacial. But as 

 they obviously carry on the story revealed by the older glacial and 

 interglacial deposits, they ought not, in my opinion, to be separated 

 from these. They form the concluding chapters of the history of 

 Pleistocene times. That great cycle of climatic oscillations which 

 commenced before the close of the Pliocene period and reached 

 down to the dawn of the present, forms one of the most remarkable 



