190 GLACIAL HISTORY. 



angular stones, efface their glacial scratches, and redeposit them 

 at a distance from the glacier proportionate to the volume of 

 the water and to its motive power. 



A stratified form will be characteristic of the beds thus brought 

 into being ; the stones will be more or less rounded, and often 

 will appear as if they had been washed, while in the moraines 

 themselves fragments of rocks of every form and size, scratched 

 and polished, angular and rounded, will be found lying with no 

 regularity, and mixed with sand, earth, and mud. 



A careful comparison of the phenomena of the Erratic for- 

 mation of Switzerland with the processes constantly going on 

 in the Swiss glaciers, shows so perfect an agreement between 

 them that they must be ascribed to the same causes ; and thus 

 the occurrence and general diffusion of Alpine rocks in the low 

 grounds of Switzerland is fully explained. 



The ramparts of stones that are found on the slopes of valleys 

 are the lateral moraines of glaciers ; and the crescent-like walls 

 have been the terminal moraines, their unstratified masses of 

 scratched and polished stones, mixed with fine debris and mud, 

 agreeing exactly with terminal moraines of the present day. 

 The representation given in fig. 360 of a portion of a moraine 

 discovered in a public place of Zurich, near the cathedral of that 

 city, shows the effect produced by existing glaciers. The strati- 

 fied beds of stones are the debris dispersed by the glacier- 

 streams, which filled up the depressions and were covered up 

 by the further advance of the glacier. Over all the hollows of 

 valleys and lakes the glaciers formed bridges, over which masses 

 of mud and earth, as well as the largest rocks, were carried for- 

 ward, and thus gradually reached great distances, and were 

 borne onwards to the summits and ridges of hills rising high 

 above the bottoms of the valleys. 



In the north of Switzerland there were five great glaciers ; in 

 Italian Switzerland only two. Their distribution is indicated in 

 the geological map *. 



The largest glacier came from the Canton of Valais, as that 



* This is based upon the map published in 1852 by Prof. A. Escher de la 

 Linth ; and for the southern slope of the Alps Prof. Heer has consulted the 

 works of M. G. de Mortillet. 



