GEOLOGY-BANKS OF PIT RIVER. 
33 
chalk, resembling very pure kaolin, derived from the decomposition of crystalline felspar. 
The lower bed is light brown, or dirty white in color, and has a slightly gritty feel between 
the fingers. 
These strata rest upon a thick bed of rolled and rounded fragments of trap, porphyry, and 
basalt, of all sizes, from masses of two and even three feet in diameter to pebbles. They are 
generally as large as one’s head, and great numbers are each a foot in diameter. 
The surface of this bed of boulders is, perhaps, twenty feet above the present surface of the 
stream; but it bears indubitable evidence of having at one time been covered by it, or, at least, 
the stones composing it, so large and clean, have been rounded where they lie by a current or 
waves of water. 
The appearance presented by this bed of boulders is different from that of any of the beds of 
volcanic conglomerate, which are so common in many parts of California and Oregon, or of 
the stratified conglomerates of the Sacramento valley, and it is undoubtedly of local origin. 
The trap which formed the greater part of the bank above is evidently of recent date ; more 
recent than the infusorial marls, and the marls more recent than the conglomerate, and the 
conglomerate an accumulation of rolled stones and pebbles, which belongs to the present 
epoch. The trap which overlies the infusorial marls composes a large part of the walls of the 
canon at this point, where it has been much cut away by the stream, and forms nearly perpen¬ 
dicular faces of several hundred feet in height. The soft nature of the underlying strata has, 
however, very much assisted in its removal. 
On the south side of the canon and overlooking it is a mountain, which forms the most 
prominent point of Stoneman’s ridge in this vicinity. It is conical in form, and has the out¬ 
line of a volcanic peak, but I found it to be composed, from base to summit, of metamorphic 
slate. 
