PHYSITOGRAPHY OF KLAMATH MOUNTAINS 155 
and north of the present limits of the lakes, and aggregating a 
thickness of two to three hundred feet. They are occasionally, 
if not generally, interstratified with beds of volcanic sand and 
ash, and sometimes coarser material, and are often overlain by 
heavy beds of tuff, and in many cases by lava flows of quite 
local origin. These diatomaceous beds are accompanied by 
marginal terraces that plainly mark the former level of the 
water, probably at its maximum height. These terraces are 
especially observable in the vicinity of Klamath Falls and along 
Lost River and elsewhere, though they have been considerably 
disturbed by faulting and volcanic eruptions. 
In the basin of the Trinity River, upon the southern border 
of the Klamath Mountains, Neocene deposits occur that Mr. 
Diller no doubt correctly correlates with the Ione of the Sacra- 
mento.’ Here, as in the Rogue River basin, they have nearly a 
conformable relation to the Cretaceous deposits wherever they 
are found in contact, and they have not yet been satisfactorily 
distinguished from each other. 
VOLCANIC ACTIVITY. 
The Cascade range.— There has been more or less discussion 
at different times regarding the character and age of the Cascade 
range. It is now generally conceded to be pre-eminently volcanic 
in character, but as to its age there is less agreement. There 
can hardly be any doubt, however, that the Cascade range as a 
mass of volcanic rocks, is the northward continuation of the vol- 
canic elements of the Sierra Nevada, and that it contains repre- 
sentatives of the lava flows that have covered so much of the 
Great Basin. 
Lavas of the region—J. E. Spurr has recently summarized 
some of the facts already known? relating to the age and succes- 
sion of lavas in the Sierra Nevada and the Great Basin. It is 
apparent that the volcanic activity of this region has extended 
over long periods of time, beginning at least with the early Ter- 
tiary (Eocene) and continuing to the present. It is therefore 
* Fourteenth Ann. Rept. U.S. Geol. Surv., Pt. I, p. 419. 
2Jour. GEOL., Vol. VIII, No. 7, 1900, pp. 621—. 
