176 PREHISTORIC EUROPE. 



in various ways. They lead only to one conclusion, and, as a 

 recent writer has remarked, 1 " correspond so wonderfully in 

 every detail to this conclusion, and this only, as to amount to 

 absolute demonstration." Among the most remarkable pheno- 

 mena are the smoothed and scratched rock-surfaces which are 

 so common a feature in upland-valleys, and which are met with 

 again and again upon hill-tops and hill-slopes, and on many 

 exposed rocks in the low grounds. These markings agree pre- 

 cisely, even to the smallest minutiae, with the similar appear- 

 ances which have been observed underneath the overhanging 

 sides of a glacier, and they are familiarly known upon the 

 bottoms and flanks of every valley in the Alps, and many other 

 regions which still support glaciers. No one doubts that such 

 smoothed and striated rocks as one sees in the valley of the 

 Unter Aar glacier and in the neighbourhood of the Grimsel, 

 were produced by the grinding action of that glacier during 

 some period of the past when it attained much larger proportions. 

 The striae are engraved by the stones and grit which are rolled 

 forward under the ice, and the rocks receive their smoothed and 

 polished surface from the finer material — the sand and mud — 

 which results from the grinding process itself. It was his 

 familiarity with tbese facts, and his knowledge that the glaciers 

 of Switzerland had in ancient times extended far beyond their 

 present limits, which enabled Agassiz to discover the true 

 meaning of the so-called " diluvial " phenomena in Scotland. 

 Another feature which receives an equally satisfactory explan- 

 ation is that of the rounded or mammillated rocks of our country. 

 These correspond exactly to the roches moutonwAes of Swiss geolo- 

 gists, so called from their having a fancied resemblance, at a 

 distance, to sheep lying down. One sees that they have been 

 produced by some heavy body passing over them in a determi- 

 nate direction. They represent what must once have been rugged 

 tors and knobs and angular excrescences, which the abrading 

 action of a glacier has softened down. Where they have not 

 suffered too severely from the influence of the weather they 



1 Quarterly Review, July 1879, p. 229. 



