CRATER LAKE, OREGON 41 



steepest slope possible without sliding. Such slopes are well 

 displayed along the western shore o})posite the island and near 

 the northeast corner of the lake under the ])alisades. At the 

 latter ])oint the rim is only 5"20 feet high, and a long slide, called 

 fron.i its shape tlie Wuie<il<iss, reaches from crest to shore. 



The best views of the rim are obtained from a boat on the lake, 

 which affords an op]K)rtunity to examine in detail the ])osition 

 and structure of the cliifs. They are composed wholly of vol- 

 canic conglomerate and streams of lava arranged in layers that 

 dip into the rim and away irom the lake on all sides. Both 

 forms of volcanic material are well exjjosed on the trail descend- 

 ing tiie inner slope, and althougii most of the cliffs are of lava 

 many are of conglomerate. 



On arriving at the water's edge, the observer is struck with 

 the fact that there is no beach. The steep slopes above the 

 surface of the lake continue beneath its waters to great depths. 

 Here and tliere upon the shore, where a rill descends from a 

 melting snowbank near the crest, a small delta deposit makes 

 a little shallow, turning the deep-blue water to pale green. 



.\s the boat skirts the western shore and passes toward Llao 

 rock, tlie layered structure of tlie rim is evident. On the Avhole 

 the lava streams predominate, although there is much conglom- 

 erate. Of all the flows exposed upon the inner slope, that of 

 Llao rock is most prominent and interesting. In tlie middle it 

 is over 1,200 feet thick, and fills an ancient vallc}^ down the outer 

 slope of the rim. Upon either side it tapers to a thin edge 

 against the upper slope of the valley, as shown in Plate 1, and 

 to the lake it presents a sheer cliff — that is, it is abruptly cut off — 

 and one wonders how much farther it may have extended in 

 that direction. Beneath the rock the outline of the valley in 

 cross-section is evident, and it rests upon many layers of older 

 lavas forming the rim down to the water's edge. The direction 

 of flow in this great lava stream forces us to believe that it was 

 erui)ted from a large volcano which once stood ui)on the site of 

 the lake. Every layer of lava in the rim is a coulee, dipping 

 away from the lake. This is especially well shown in the canyon 

 of Sun creek, cut in its outer slope. The sections of these radi- 

 ating flows exposed upon the inner sloi)e of the rim all tell the 

 same story as to their source. By projecting the lavas in their 

 course toward a common center we can reconstruct in fancy the 

 great volcanic mountain that once occupied the place of the 

 latter— that is, Mount Mazama— and, like Shasta or Rainier, 



