56 



SCIENCE 



[N. S. Vol. XLI. No. 1045 



California, nor cut into parallel ridges by 

 large faults, yet in places along the coast, 

 as at Coos Bay, the thinner bedded Eocene 

 has been folded and compressed into a 

 vertical position. The later intermittent 

 uplift during the Quaternary is recorded 

 by a series of elevated beaches cut more or 

 less deeply on the west slope by the ocean 

 waves. 



THE CASCADE RANGE 



The Cascade range is essentially a vol- 

 canic range stretching from Lassen Peak 

 in California to Mt. Rainier in Washington, 

 a distance of 450 miles. At both ends the 

 lavas lap up on to the uplifted mountains 

 of older rocks, the Sierra Nevada in Cali- 

 fornia and the northern Cascades in Wash- 

 ington, but between these two from the 

 Columbia River in Washington to the Pit 

 River in California, for a distance of 

 nearly 300 miles, the range is composed 

 largely, if not wholly, of igneous rocks that 

 have escaped from a great belt of volcanoes 

 that form the range. The summit of the 

 range is an irregular plateau strewn with 

 many lava and cinder cones, of which each 

 one marks the site of a volcanic orifice 

 tributary to the upbuilding of the range. 



Where best developed, as shown in the 

 Klamath and Columbia river sections, the 

 body of lava forming the range is on the 

 average probably about 4,000 feet in thick- 

 ness, but in the greater volcanoes like 

 Hood, Jefferson, Mazama, Shasta and Las- 

 sen it rises to accumulations of 6 to 10,000 

 feet in thickness. The later foundations 

 of the Cascade range were laid in the Ore- 

 gon embayment during the Cretaceous and 

 early Tertiary times, possibly before the 

 ranges were distinctly outlined. The Ter- 

 tiary volcanic effusions began in Oregon 

 west of the Cascade range during the 

 Eocene and possibly a little later in the 

 same epoch eruptions began in the base of 

 the Cascade range. During the later Ter- 



tiary the volcanic activity was greatest and 

 the bulk of the range, though partly up- 

 lifted, was in equal or perhaps even greater 

 measure upbuilt by flows of viscous ande- 

 sitie lavas with much ejected material. 

 Basalts are common and some acid lavas 

 are known, but the great bulk of the range 

 is andesite in strong contrast with the great 

 lava plains east of the Cascades, where the 

 thin basalt flows spread out horizontally 

 like sheets of water. The change from the 

 plain to the mountain slope at the eastern 

 base of the Cascade range is abrupt and 

 distinct, and due, for the most patt, to the 

 fact that the stiff viscous andesitic lavas 

 were able to build up steep slopes while the 

 superheated and highly liquid basaJts 

 spread out like water along the irregular 

 mountain front. 



After the close of the Tertiary the vol- 

 canic activity waned, although eruptions 

 occurred to within the historic period and 

 possibly even to the present day if the out- 

 bursts from the summit of Lassen Peak de- 

 velop so as to involve molten material. 



However that may be, there is no doubt 

 that the Cinder Cone and its lava field 10 

 miles northeast of Lassen Peak resulted 

 from one or more eruptions within a cen- 

 tury or two. In 1843 both Baker and St. 

 Helens were in violent eruption, ejecting 

 large quantities of ashes, of which Fre- 

 mont obtained samples collected at the time 

 of the eruption. There is also well-attested 

 authority that eruptions occurred on Mt. 

 Baker in 1854, 1858 and 1870. In general, 

 however, the volcanoes of the Cascade 

 range are considered extinct, and the up- 

 building of the Cascade range completed 

 as far as the actual accumulation of lava 

 is concerned. 



While the great altitude of the range is due 

 chiefly to the piling up of lavas, a consider- 

 able portion is due to actual uplift, for in 

 the Cretaceous of the Rogue River valley 



