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 an# 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. 



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