372 CRATER LAKE, OREGON. 



In addition to the strong contrast between the outer and inner slopes 

 of the rim the map shows the occurrence of a number of small cones 

 upon the outer slope of the great cone. These adnate cones are of 

 peculiar significance when we come to consider the volcanic rocks of 

 which the region is composed. The rim is ribbed by ridges and spurs 

 radiating from the lake, and the head of each spur is marked by a 

 prominence on the crest of the rim. The variation in the altitude of 

 the rim crest is 1,460 feet (from 6,759 to 8,228) with seven points rising 

 above 8,000 feet. The crest generally is passable, so that a pedestrian 

 may follow it continuously around the lake, with the exception of short 

 intervals about the notches in the southern side. At many points the 

 best going is on the inner side of the crest, where the open slope, gener- 

 ally well marked with deer trails over beds of pumice, affords an unob- 

 structed view of the lake. 



Eeference has already been made to the glacial phenomena of the 

 outer slope of the rim. There are scattered bowlders upon the surface, 

 aufl also in jiiles of glacial moraine (fig. 7) which contain besides bowl- 

 ders much gravel and sand. Such glacial drift is spread far and wide 

 over the southern and western portion of the rim, extending down 

 the watercourses in some cases for miles to broad plains through wliich 

 the present streams have carved the deep and picturesque canyons 

 already observed on the ascent. At many points the lavas are well 

 rounded, smoothed, and striated by glacial action. This is true of the 

 ridges as well as of the valleys, and the distribution of these marks is 

 coextensive with that of the glacial detritus. 



A feature that is particularly impressive to the geologist making a 

 trip around the lake on the rim crest is the general occurrence of 

 polished and striated rocks, in place on the very brow of the clift' over- 

 looking the lake. The best displays are along the crest for 3 miles 

 northwest of Victor Rock, but they occur also on the slopes of Llao 

 Eock, Eound Top, Kerr Notch, and Eagle crags, thus completing the 

 circuit of the lake. On the adjacent slope toward the lake the same 

 rocks present rough fractured surfaces, showing no strise. The glacia- 

 tion of the rim is a feature of its outer slope only, but as shown in 

 figure 8, it reaches up to the very crest. The glaciers armed with 

 stones in their lower parts, that striated the crown of the rim, must 

 have come down from above, afid it is evident that the topographic 

 conditions, of to-day afford no such source of supply. The formation 

 of glaciers requires an elevation extending above the snow line to 

 afford a gathering ground for the snow that it may accumulate, and 

 under the influence of gravity descend to develop glaciers lower down 

 on the mountain slopes. During the glacial period Crater Lake did 

 not exist. Its site must then have been occupied by a mountain to 

 furnish the conditions necessary for the extensive glaciation of the rim, 

 and the magnitude of the glacial phenomena indicates that the peak 

 was a large one, rivaling, apx^arently, the highest peaks of the range. 



