22 Notices of Memoirs, 



lain by finely stratified fossiliferous clays, or sometimes by a very 

 coarse Upper Boulder-clay. Mucli still remained to be done in the 

 working out of the history of these deposits in detail, but the general 

 succession of geological changes which they indicated were neverthe- 

 less sufficiently ascertained. 



Geologists were agreed that the observed phenomena could only 

 be explained by reference to what is now taking place in arctic and 

 alpine regions. The rounded contour of our hills, the flutings and 

 sculpturings of our vallej^s, the scratched and polished rock-surfaces 

 that everywhere abounded, bore emphatic testimony to the former 

 passage of a great sheet of ice, under which, at some distant period, 

 these islands of ours, in common with the high latitudes of Europe, 

 Asia, and America, lay buried — only the loftier mountain tops peer- 

 ing above the desolate waste. And in like manner did the accumu- 

 lations of sand and gravel and clay, and the pell-mell heaps of the 

 Upper Boulder earth, testify to the subsequent presence of the sea 

 over certain areas of the same regions. 



Mr. Geikie stated that during the early stages of the Glacial 

 epoch the surface of our country, by the constant grinding action of 

 the great ice-sheet, came to assume certain characters which are 

 still very legible. He showed that the general trend of the ruts and 

 scratches impressed upon the rocks by the passage of the glaciers 

 was, in the northern hemisphere, from north to south, but that the 

 form of the ground often had considerable influence in turning them 

 from that general direction. Thus in our own country they were 

 found to radiate downwards from the high grounds, following the 

 lines of the principal valleys. 



During the continuance of this Arctic condition of our country, 

 the waste of the underlying rocks must have been considerable. 

 Mountains of schist had been in some measure deprived of the 

 outlines which, under usual atmospheric action, they must have 

 assumed. Hills of shattered and much jointed greywacke, which 

 ought to rise up in broken, serrated, and peaky tors, showed instead 

 a rounded and hummocky contour. Valleys which, from the nature 

 of their strata, we should have expected to present steep or vertical 

 walls, have been moulded into smooth and undulating hollows. 

 Glens, at one time roughened with countless crags, and bristling 

 with jagged points of rock, have had their sharp angles and rude 

 corners cut away — the present ruinous and tumbled aspect of many 

 of our Highland glens being due to subsequent atmospheric waste, 

 which was gradually effacing the traces of Glacial action. The 

 waste material that resulted from all this scooping and grooving 

 and planing went to form the Boulder-clay. Some of it gathered 

 underneath the great glacier as a moraine profonde — some of it was 

 carried out to sea by icebergs. 



The character and mode of accumulation of the true Lower Boulder- 

 clay were next described. As the " ground moraine" of the old ice- 

 pheet, it gathered most abundantly over the surface of the lowlands, its 

 occurrence at considerable elevations being the exception to the rule. 

 It was remarked that in districts where the marine drift occurred, 



