Febeuaey 7, 1902.] 



SCIENCE. 



207 



ORIGINAL CONDITION OF MT. MAZAMA. 



Thus far the existence of an original Mt. 

 Mazama has been assumed. The evidence 

 on which this assumption is based may be 

 briefly stated as follows : The inner slope 

 of the rim presents sections of the broken 

 lava flows which radiate from the lake and 

 were evidently effused from a source higher 

 in each case than the respective flow in the 

 rim. If the flows of the rim were to be 

 restored to their original size by extending 

 them inwards from the rim, as they once 

 certainly did, they would converge to a 

 common source and make a volcano which 

 would occupy the place of the caldera and 

 make a prominent peak, Mt. Mazama. 



The peak must have had a crater similar 

 in character to that of Wizard Island, for 

 it was the source of much fragmental ma- 

 terial spread in all directions upon the 

 mountain slope. 



The former existence of Mazama Peak 

 is indicated also by the radial series of 

 dikes which cut the rim. They evidently 

 originated in the pressure of the column 

 of molten material in the chimney of a 

 volcanic peak rising some distance at least 

 above the rim. 



The most convincing evidence of the ex- 

 istence of Mt. Mazama on the site of Crater 

 Lake is to be found in the glaciation and 

 drainage of the rim. The radiating 

 glaciers, which in their descent scored the 

 crest of the rim, could have come only from 

 a central peak. The records of the ice and 

 water drainage from the peak in the topog- 

 raphy of the rim are unmistakable. 



There can be no reasonable doubt as to 

 the former existence of Mt. Mazama, but 

 its shape and size are more difficult to de- 

 termine. Mt. Mazama is composed largely 

 of lavas similar to those of Mt. Shasta, and 

 from the slopes of that famous peak we 

 may draw an inference as to those of Mt. 

 Mazama. Mt. Shasta, unlike Mt. Mazama, 

 does not stand on an elevated platform. It 



rises with a majestic sweep of 11,000 feet 

 from gentle slopes about its base, gradually 

 growing steeper upwards to the bold peak. 

 At the height of 8,000 feet it has about the 

 same diameter as Mt. Mazama at an equal 

 elevation in the rim of Crater Lake. 

 Above this Mt. Shasta rises over 6,300 feet. 

 The prominence of Mt. Mazama as a drain- 

 age center is quite equal to that of Mt. 

 ■ Shasta, but its slopes on the rim of Crater 

 Lake, ranging from 10 to 15 degrees, are 

 scarcely as great as those of Mt. Shasta 

 at a corresponding elevation. On the other 

 hand, the .canyons of Sun and Sand creeks 

 on Mt. Mazama are more profound and 

 have been much more deeply glaciated 

 than any of those on Mt. Shasta. It there- 

 fore appears reasonable to suppose that 

 Mt. Mazama had an altitude at least as 

 great and possibly greater than that of 

 Mt. Shasta (14,380). 



DEVELOPMENT OF MT. MAZAMA. • 



Mt. Scott is only a large adnate cone to 

 Mt. Mazama. It belongs to the same cen- 

 ter and holds essentially the same relation 

 to it as Shastina does to Shasta. The 

 slopes of Mt. Mazama reach to the plains 

 at its eastern base, and it is one of the 

 largest members in the composition of that 

 range. 



The beginnings of Mt. Mazama are now 

 deeply buried beneath the lavas of the 

 range, including those displayed on the 

 lower slopes of the great caldera beneath 

 the water of Crater Lake. The earliest 

 lavas now visible are those of the southern 

 and western lake border, and when they 

 were erupted the volcano was normally 

 active, sending out with its streams of lava 

 large contributions of fragmental material 

 to make the heavy conglomerates of the 

 older portion of the rim. The many suc- 

 ceeding flows of andesite and layers of 

 conglomerate built up the mountain slope 

 to the crest of the rim upon the southern 



