30 GEOLOGY — WESTERN RANGE OF 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 mountahi 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, but 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, but represented the bed to be 

 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, but no tertiary rocks are known to 

 exist within many miles of this locality ; and the lignites of Santa Clara on one side and Coose 

 bay on the other, are the nearest deposits of what could, with any propriety, be 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, but that could not be 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 be 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 felspathic 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 be 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 bare of vegetation, and covered with piles of lava, or slopes of 

 ashes. 



