177 



CHAPTER XIII. 



GLACIAL HISTORY. 



THE section at Diirnten given in fig. 328 (p. 150) shows that 

 the lignites at that place are covered by a great deposit of stra- 

 tified gravel and sand, upon the surface of which isolated blocks 

 are found. At Utznach the lignites (fig. 329, p. 152) are also 

 covered by gravel and sand, and separate blocks occur on the 

 surface of the deposits. Beds of stratified pebbles and sand are 

 seen continually in the gravel-pits opened for mending the roads; 

 they prove that these deposits are spread over the low grounds 

 of Northern Switzerland, and that the formation exemplified at 

 Diirnten and Utznach is distributed over a great portion of the 

 lower district of the country. This formation has been described 

 as Stratified Diluvium [and also as Drift] . It consists of more 

 or less rolled fragments, which generally vary in size from that 

 of a walnut to that of a man's fist, lying in more or less hori- 

 zontal beds, sometimes alternating with bands of sand. The 

 pebbles mostly have belonged to rocks which are not found 

 in the Swiss plains, but which originally appertained to the 

 neighbouring Alps. In the Canton of Zurich the gravel-pits 

 contain a mass of red pebbles, composed of the sernifite of the 

 Glaris Alps; with these are fragments of limestone, representing 

 the various calcareous formations of the high Swiss mountains. 

 In the vicinity of the Lake of Constance and the Rhine, as near 

 Diessenhofen, Stein, &c., everywhere are found vast beds of 

 rolled pebbles, the materials of which are derived from the valley 

 of the Rhine. The plain between Thun and Thierachern and up 

 to the shore of the Lake of Thun is covered with masses of sand 

 and pebbles, the origin of which may be traced to the neigh- 

 bouring Alps ; and on the shores of the Lake of Geneva gravel 

 VOL. ii. N 



