30 
GEOLOGY-WESTERN RANGE OE SIERRA NEVADA. 
LOCAL GEOLOGY. 
Our journey over the base of Lassen’s butte to the basin of Pit river was productive of little' 
geological information, except of the monotonous prevalence of recent volcanic rocks over all 
that portion of this mountain chain which we traversed. 
From Fort Reading to McCumber’s, some twenty-five miles, plateaus and ridges of dark 
vesicular trap extend in unbroken and‘unvaried succession. Here we had an inkling of some 
facts of high geological interest, hut were unable to remain long enough to settle the questions 
raised by the information received. Mr. McCumber has found coal, as he says, of good quality, 
in the hills a few miles distant from his rancho. Of this coal he had then no specimen, and 
could tell me nothing of the character of the associated rocks, hut represented the bed to he 
thick and extensive. 
This information, though vague and unsatisfactory, was, as it seemed to me, highly important, 
as proving the existence of beds of coal at this elevation and distance from the coast. 
McCumber’s flat is about 4,000 feet above the sea, and the deposits of coal represented to be 
several hundred feet higher, probably at least 4,500 feet above the sea level. It is, perhaps, 
possible that the tertiary lignites of the coast recur here, hut no tertiary rocks are known to 
exist within many miles of this locality; and the lignites of Santa Clara on one side and Coose 
hay on the other, are the nearest deposits of what could, with any propriety, he termed coal. 
Taken in connexion with the fact of the occurrence of carboniferous limestone a few miles 
northwest from McCumber’s, and this limestone having a rapid easterly dip, indicate at least a 
possibility that the coal of this vicinity may be carboniferous. A single hand specimen would 
have decided the question, hut that could not he obtained; and since the promise of Mr. McCumber 
to send into Fort Reading specimens of the coal was not kept, the problem is yet unsolved, 
whether the tertiary lignites of California and Oregon are the only coals found on the Pacific 
coast. 
If these carbonaceous beds should prove to be of the same age with those referred to, the fact 
would he scarcely less important, and would perhaps materially aid us in the solution of some 
of the problems which the geology of the far west still presents. 
After leaving McCumber’s, we found the dark vesicular trap, which prevails over so large an 
area around Fort Reading, mingled with, and in many places entirely superseded by, volcanic 
rock of different character. Immediately east of McCumber’s we passed a surface, a mile or more 
in extent, over which the vegetable soil covered rolled and rounded fragments of pumice and 
a light-colored felspatliic lava. These boulders had, apparently, formerly occupied the broad 
bed of a water-course, from which the supply of water had long since been cut off by some of 
the convulsions of this volcanic region. That this change of course in the stream was not of 
recent date, is proved by the accumulation of soil on the surface and the dense growth of large 
trees which it supported. 
Lassen’s butte is evidently a volcanic cone, and one whose fires have not been long extin¬ 
guished. Its summit is distinctly crateriform, as will he seen from the accompanying cut, and 
is capped with perpetual snow, and has an altitude of about 9,000 feet. Below the snow line 
for 1,000 feet the mountain is hare of vegetation, and covered with piles of lava, or slopes of 
ashes. 
