"POSTGLACIAL FORMATIONS" OF SCOTLAND 669 



valley. The deposits overlying that bowlder- clay have nevertheless 

 been classified as postglacial, although it is obvious that they must 

 be of much greater antiquity than the alluvia and peat resting upon 

 the valley moraines and fluvio-glacial accumulations of our district 

 ice-sheets in Scotland. The fact is, the term "postglacial" is quite 

 misleading, and ought never to appear in any general classification 

 of formations. 



Continued research in Europe, America, and Asia has demon- 

 strated that the so-called Ice Age was not one long uninterrupted 

 period of glacial conditions, but an extensive cycle of alternating 

 cold and genial conditions, which commenced before the close of 

 Pliocene times and endured down to the very dawn of the present. 

 I believe, therefore, that the upper members of the PKocene system 

 will before long be included in the Pleistocene, and that the latter 

 will embrace all the glacial and interglacial stages. In a word, 

 the term "Pleistocene" will eventually cover every accumulation 

 formed during the great cycle of alternating climatic conditions. 

 This being so, it will certainly include most of the deposits which 

 in our and other glaciated regions are commonly termed postglacial. 



For the present, however, let us consider the epoch of the "Dis- 

 trict Ice-Sheets and Mountain-Valley Glaciers," to be the closing 

 phase of the Ice Age in Scotland, and proceed to inquire into the 

 history revealed by the co-called "postglacial deposits" of our 

 country. The most representative of these accumulations are our 

 raised beaches, estuarine and 'fluviatile terraces, lacustrine alluvia, 

 and peat-mosses. 



RAISED BEACHES, ETC. 



At least three well-marked raised beaches are visible at many 

 places upon our coastlands. Of these the oldest occurs at a height 

 of 100 to 135 feet above the present sea-level. There can be no 

 doubt that this beach belongs to the true glacial series, and I only 

 refer to it in this place because the phenomena connected with it 

 are similar in many respects to those associated with some of the 

 younger "postglacial" raised beaches. In the great valleys of the 

 Forth and Tay, for example, it forms extensive terraces, which, 

 as they are followed inland, gradually rise to higher and higher 

 levels and merge into fluvio-glacial gravels, while these last even- 



