320 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 3 5 



lava flow implies that the volcano changed from an explosive type 

 to a quiet eruptive type. The occurrence of dacite instead of an- 

 desite during the late stages of mountain growth signifies internal 

 changes. Each successive layer of volcanic material exposed in the 

 rim required time to accumulate, and each one that was followed by 

 glaciation required time to cool before the process of snow accumu- 

 lation could start. 



Thus the glacial record of an extinct volcano helps to establish 

 time intervals in volcano-building and contributes to the knowledge 

 of earth history. 



