ANCIENT MORAINES. 729 



wanting. In some places the seams of harder 

 rock stood out for a quarter of an inch or so 

 above adjoining decomposed surfaces ; in such 

 instances the dike alone retained the glacial 

 marks, which had been worn away from the 

 softer rock. 



The old moraines were numerous and ad- 

 mirably well preserved. Agassiz examined 

 with especial care one colossal lateral moraine, 

 standing about two miles below the present 

 terminus of the ice and five hundred feet 

 above the sea-level. It consisted of the same 

 rocks as those found on the present terminal 

 moraine, part of them being rounded and 

 worn, while large, angular boulders rested 

 above the smaller materials. This moraine 

 forms a dam across a trough in the valley 

 wall, and holds back the waters of a beautiful 

 lake, about a thousand feet in length and five 

 hundred in width, shutting it in just as the 

 Lake of Meril in Switzerland is held in its 

 basin by the glacier of Aletsch. There are 

 erratics some two or three hundred feet above 

 this great moraine, showing that the glacier 

 must have been more than five hundred feet 

 thick when it left this accumulation of loose 

 materials at such a height. It then united, 

 however, with a large glacier more to the 



