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ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 3 5 



Figure 7. — Index map of the Crater Lake Region. 



and striated rock surfaces (pi. 3, fig. 1).* The existence of these 

 striae on the surface lavas indicates that glacial ice crossed this 

 portion of the rim following the last lava eruption. 



When standing on the striated surface close to the edge of the 

 cliff, it is possible to look down approximately 40 feet to another 

 glacially polished surface. Upon investigation it is discovered that 

 these glacial scratches are covered with 10 feet of boulder till, and 

 that the till is, in turn, capped with 30 feet of lava. This relation- 

 ship is best shown in plate 3, figure 2. How did the glacial material 

 become sandwiched in between flows of lava? The answer is 



* All photographs, unless otherwise credited, are official pictures of the National Pari? 

 Service. 



