•204 



SCIENCE. 



[N. S. Vol. XV No. ;-(71. 



ley. The Cascade Range throughout, a 

 large part of its extent rests upon Cre- 

 taceous rocks and is associated in Oregon 

 and California with a depression in the 

 older rocks between the Klamath Mountains 

 on the one hand and the Blue Mountains 

 and Sierra Nevada upon the other. This 

 depressed area beneath the lavas of the 

 Cascade Range must not be regarded 

 primarily as a region of subsidence. Its 

 chief movement since the Cretaceous has 

 been upward. It has been raised above the 

 sea. The Klamath and Blue Mountains, 

 as well as the Sierra Nevada, however, have 

 been elevated so much more that the region 

 in question would appear on the surface as 

 a depression were it not filled with lava. 

 The depression is so deep where the Cas- 

 cade Range is cut across by the Klamath 

 and Columbia rivers that the bottom of 

 the lavas forming the bulk of the range is 

 not reached. However, at the ends of the 

 range the older rocks rise to form a more 

 or less elevated base for those parts of the 

 range, and at Mt. Shasta as well as on the 

 divide between the Rogue and Umpqua 

 rivers, where an arch of the older rocks ex- 

 tends northeasterly from the Klamath 

 Mountains towards the Blue Mountains of 

 eastern Oregon, the Cascade Range gets so 

 close to the western side of the depression 

 that the lavas lap up over the arch of older 

 rocks rising to the westward. At various 

 points of the range granolitic rocks, such 

 as gabbro and diorite, occur, but the deep 

 erosion at these points may have reached 

 the granolites corresponding to the lavas 

 of the up53er portion of the range. 



CASCADE RANGE DURING THE EOCENE. 



There can be no reasonable doubt that 

 fossiliferous Cretaceous rocks of marine 

 origin are widely distributed beneath the 

 Cascade Range from Lassen Peak to the 

 Columbia, and that during the Chico 

 epoch the whole area was beneath the sea. 



At the close of the Chico important 

 changes occurred in the distribution of 

 land and sea. Northern California, as well 

 as southern Oregon, was raised above the 

 sea and subjected to extensive erosion be- 

 fore the subsidence which admitted the sea 

 during the early part of the Tertiary 

 as far southeast as Roseburg, Oregon. 

 The marine deposits of the Eocene 

 epoch in the vicinity of Roseburg run 

 under the Cascade Range, but have not yet 

 been found upon the eastern side. The 

 conglomerates of the Eocene, like those of 

 the Cretaceous, contain many pebbles of 

 igneous rocks, but they are of types com- 

 mon to the Klamath Mountains and rare 

 or unknown among the lavas exposed in 

 the Cascade Range. During the Eocene 

 in the Coast Range of Oregon there was 

 vigorous volcanic activity,* but the record 

 of such activity, if such existed, has not 

 yet been found in the Cascade Range. That 

 volcanoes were active along the range dur- 

 ing the Eocene is rendered more probable 

 although not yet conclusive by Dr. J. C. 

 Merriam's discovery of Eocene volcanic de- 

 posits in the John Day region, f 



CASCADE RANGE DURING THE MIOCENE. 



There can be no doubt, however, that 

 during the Miocene| the volcanoes of the 

 Cascade Range were most active and the 

 greater portion of the range built up, al- 

 though it is equally certain that volcanic 

 activity continued in the same region at a 

 number of points almost to the present 

 time. While it may be presumed that the 

 volcanoes of the Cascade Range are extinct, 

 there are many solfataras, hot springs and 

 f umeroles, showing that the volcanic energy 

 of the range is not yet wholly dissipated. 



* U. S. Geol. Survey, Seventeenth Annual Re- 

 port, Part I., p. 456. 



t Bulletin Geol. Dept. of Univ. of Cal., Vol. 2, 

 No. 9, p. 285. 



tU. S. Geol. Survey, 20th Annual Report, 

 1898-9, Part III., p. 32. 



