Fkbeuaey 7, 1902.] 



SCIENCE. 



205 



All the peaks of the Cascade Range were 

 once active volcanoes, and from them came 

 most of the lava of the range. Each great 

 volcano was surrounded within its prov- 

 ince, at least during the later stages, by- 

 numerous smaller vents from which issued 

 the lava that filled up the intervening 

 spaces and built up the platform of the 

 range. 



All of the great volcanoes of the range 

 probably had their beginning in the Mio- 

 cene. Many of them, like Lassen Peak and 

 Mount Shasta, continued their activity into 

 the Glacial Period and have suffered much 

 erosion since they became extinct. In this 

 manner important structural differences 

 have been brought to light among the peaks 

 about the headwaters of the Umpqua, 

 Rogue river and the Klamath, and these 

 may be noted as throwing some light upon 

 the history of Mt. Mazama, whose wreck 

 we are to consider. 



UNION PEAK. 



Union Peak (7,881 feet) is on the sum- 

 mit of the Cascade Range in Oregon about 

 50 miles north of the California line, and 

 8 miles southwest of Mt. Mazama. It is 

 a sharp conical peak rising about 1,400 feet 

 above the general summit of the range. 

 About the base upon the east and west 

 sides, as well as upon its very summit, are 

 remnants of the original tuff cone, but the 

 mass of the peak exposed upon all sides is 

 solid lava. The molten material did not 

 sink away after the final eruption. The 

 volcanic neck resulted from the cooling of 

 lava within the cinder cone in the very top 

 of the volcanic chimney, and Union Peak 

 to-day shows us the neck stripped of its 

 cinder cone. 



MT. THIELSEN. 



Mt. Thielsen (9,250 feet), the Matter- 

 horn of the Cascade Range, is 12 miles 

 north of Mt. Mazama and rises about 2,000 

 feet above the general summit of the range. 



It is built up of brightly colored red, yel- 

 low and brown layers of tuff interbedded 

 with thin sheets of lava, and the whole is 

 cut by a most interesting network of dikes 

 radiating from the center of the old vol- 

 cano. No trace of a volcanic neck is pres- 

 ent; the peak is but a remnant carved out 

 of the lava and tuff cone surrounding the 

 vent. After the final eruption the molten 

 material withdrew from the cone before 

 consolidation so as to leave no volcanic neck 

 corresponding to that of Union Peak. The 

 subsidence after eruption within the chim- 

 ney of Mt. Thielsen must have been over 

 1,000 feet, for the sheets of lava effused 

 from that vent reach more than 1,000 feet 

 above the central portion of the peak. 



MOVEMENT IN MT. MAZAMA. 



To simplify matters it seems best at this 

 point to anticipate some of the conclusions 

 to be reached and state that upon what is 

 known as the rim of Crater Lake there once 

 stood a prominent peak to which the name 

 Mt. Mazama has been given. The crowning 

 event in the volcanic history of the Cascade 

 Range was the wrecking of Mt. Mazama, 

 which resulted from a movement similar to 

 that just noted in Mt. Thielsen but vastly 

 greater in its size and consequences. It 

 culminated in the development of a great 

 pit or caldera, which for grandeur and 

 beauty rivals anything of its kind in the 

 world. 



Mt. Mazama is practically unknown to 

 the people of Oregon, but they are familiar 

 with Crater Lake, which occupies the de- 

 pression within the wreck of the great 

 peak. The destruction of the mountain re- 

 sulted in the formation of the lake, and 

 the remnant of Mt. Mazama is most readily 

 identified when referred to as the 'rim of 

 Crater Lake.' 



CASCADE EANGE SUMMIT. 



The Cascade Range in southern Oregon 

 is a broad irregular platform, terminating 



