24 Notices of Memoirs, 



ceeded to examine the nature and degree of subaerial waste experienced 

 since the close of the great age of ice. Every geologist was familiar 

 with the glaciated outline of the elevated regions of our country. The 

 rounded crags, the smoothed and fluted hill sides, and the finely striated 

 rock-surfaces were characters so well-known that he had only to 

 mention them. When he said that these were to be met with every- 

 where, of course he did not mean that every declivity would show 

 its ice-mouldings, every crag exhibit roches moutonnees, or every ex- 

 posed surface of rock exhibit a series of striations. Such must, no 

 doubt, have been the case when the great ice-sheet first disappeared, 

 but during the long ages that had since elapsed chemical decomposi- 

 tion, frost, and rain had succeeded in obliterating many traces of the 

 ancient glaciers. Notwithstanding all this, however, the memorials 

 of the former presence of a vast body of ice were so abundant that 

 we could not but conclude that the solid rocks of our mountains had 

 suffered comparatively little waste since that covering of ice had 

 vanished. A visitor from Alpine countries, where perennial snows 

 and glaciers abounded, would see little in the outline of our Scottish 

 mountains with which he was not familiar. The finer touches of tho 

 great ice chisel would oftentimes indeed be wanting, but its broad 

 effects would all be there, reminding one who wished to be fanciful, 

 of those ancient sculptures from which the hand of time had effaced 

 the delicate finish of the artist but had been powerless to destroy his 

 design. 



Mr. Geikie next considered the present aspect of the Boulder- 

 clay. He said that in our valleys and straths we could read the 

 history of a Glacial period with as little difficulty as we deciphered 

 its records at higher levels. It was admitted that the subaerial 

 waste experienced by the Boulder-clay had been great, but when we 

 came to estimate what effect this erosion had had in modifying the 

 general aspect of that deposit it appeared to be scarcely appreciable. 

 The greatest waste experienced by the Till took place during the 

 growth of the marine drifts. Waves and currents in narrow straits 

 and open seas had often made havoc of the Boulder-clay, while in 

 the fiords and other sheltered regions the some degree of waste could 

 not be effected. And the configuration thus given to the lower Till had 

 not been obliterated by the atmospheric forces, although these had been 

 so long employed in its reduction. If frosts and rains and rivers bad 

 been unable to deprive the lower Till of the general aspect it assumed 

 on the re-elevation of the land, they had been just as powerless to 

 efface the external character of the upper or marine drifts. So per- 

 fect were the forms of mounds and kaims of sand and gravel that 

 these were capable of being classified and described by reference 

 to the various kinds of bars and banks of analogous materials which 

 were gathering on the bed of our own seas at the present day. But 

 just as it was seen that the Boulder-clay had been extensively de- 

 nuded by atmospheric agents, so we learned that the marine drifts 

 had undergone no inconsiderable degree of erosion. From some 

 valleys they had well nigh vanished ; in others the kaims had been 

 obliterated and their materials re-assorted bv the streams and rivers. 



