James GeUde — On Changes of Climate. 29 



Karnes it is doubtful whether there were any glaciers entering the sea ; 

 if this was so, the supply of glacial mud would be stoj)ped, and the 

 absence of glacial clays from the interior parts of the country may 

 thus be accounted for. It is true that much mud would result from 

 the denudation of the Till ; but we may be quite sure that the currents 

 which heaped up the gravel ridges would not permit the fine mud to 

 settle down save at great distances from the land. The deposition 

 of the shelly clays took place at a time when glacial mud was being 

 poured into every quiet fiord on our coast ; but this was during the 

 period of re-elevation. From these and other considerations, which 

 want of space forbids me to enter upon, I think it is most probable 

 that the shelly clays belong as a whole to a later date than the 

 Kames, and were deposited under colder conditions of climate than 

 the last-mentioned accumulations. At the time some of the shell- 

 beds were forming glaciers reached the sea in many of our firths, 

 and icebergs and coast-ice floated about. 



The re-elevation of the land continued, and erelong glaciers ceased 

 to reach the sea. An amelioration of climate had again ensued. 

 Slowly the glaciers crept up the valleys, leaving behind them a 

 number of moraines, some of which are finely preserved. 



The later stages of the history are well known. Scotland pro- 

 bably became connected with the continent across the upraised bed of 

 the North Sea. By this time the climate had greatly ameliorated, 

 and the country, along with a large part of Northern Europe, became 

 covered with dense forests. 



The subsequent depression of the land and the insulation of Britain 

 must have tended still further to temper the cold of winter, although 

 at the same time the warmth of the summers would also be some- 

 what reduced. The decay of the ancient forests probably dates its 

 beginning from this period. The more recent raised beaches indi- 

 cate still later changes in the relative level of land and sea, but a 

 consideration of these is beyond the purpose of this paper. 



Since the time that the shelly clays were deposited down to the 

 present we have no trace in the post-Glacial beds or recent alluvia 

 of any warm climate having intervened. From the close of the 

 Glacial period the climate has regularly and successively become 

 milder : neither post-Glacial nor recent alluvial deposits give the 

 slightest hint that any considerable oscillations of temperature have 

 taken place since then. 



To sum up, then, the results at which we have arrived, I shall in 

 a few words recapitulate the points which I have endeavoured to 

 bring prominently forward. 



1st. The TilP of Scotland with its intercalated beds indicates a 

 vast lapse of time, during which there were several great revolutions 

 of climate, how many we do not know. 



^ I think it much to he desired that the terms Till and Boulder-clay should not be 

 applied to one and the same deposit. If Till were taken to mean simply the material 

 collected underneath land-ice, the moraine profonde of Swiss geologists, it would 

 save confusion. Boulder-clay could then be applied to those more or less stratified 

 clays with boulders which have been deposited in water. In my previous paper I ■ 

 have used the two terms interchangeably ; in the present paper, however, and in 

 future, I will apply them in the manner just suggested. 



