I 



LETTER FROM AG A SSI Z TO PEIRCE. 757 



extending for more than twenty-five degrees 

 f latitude, is a continuous glacier bottom, 

 owing plainly that for its whole length 

 e great southern ice-sheet has been retreat- 

 ng southward in it. I could find nowhere 

 any indication that glaciers descending from 

 the Andes had crossed this valley and reached 

 the shores of the Pacific. In a few brief lo- 

 calities only did I notice Andean, i. e. vol- 

 Icanic, erratics upon the loose materials fill- 

 ing the old glacier bottom. Between Curicu 

 and Santiago, however, facing the gorge of 

 Tenon, I saw two distinct lateral moraines, 

 parallel to one another, chiefly composed of 

 volcanic boulders, resting upon the old drift, 

 and indicating by their position the course of 

 a large glacier that once poured down from 

 the Andes of Tenon, and crossed the main 

 valley, without, however, extending beyond 

 the eastern slope of the Coast Range. These 

 moraines are so well marked that they are 

 known throughout the country as the cerillos 

 of Tenon, but nobody suspects their glacial 

 origin ; even the geologists of Santiago assign 

 a volcanic origin to them. What is difficult 

 to describe in this history are the successive 

 retrograde steps of the great southern ice- 

 field that, step by step, left larger or smaller 



