OUTLINE OF THIS MONOGRAPH. XXXV 
The ore deposits have been laid open to the hand of man chiefly by erosion, which has 
stripped off the overlying rocks and has carved deep valleys through the metalliferous deposits. 
It is estimated that since the beginning of disturbance 15,000 feet of sediments have been removed 
from that part of the Aspen district which lies east of the Castle Creek fault. The most recent 
of the erosive processes was glaciation. There is evidence that a general ice sheet at one time 
covered the whole of the Aspen district, moving over hill and valley westward from the Sawatch 
This has left its trace in the rounded and fluted forms into which the hilltops are carved, and in 
deposits of morainal material, generally finely ground. Subsequently this ice sheet shrank to 
smaller dimensions, so that there resulted local glaciers which followed the course of preexisting 
valleys and carved them into their present forms. These glaciers have left lateral and terminal 
moraines. At about this period, also, there existed in the Aspen Valley temporary lakes, probably 
resulting from damming-up of the glacial waters. 
