4/0 PHYSICAL GEOGRAPHY. 



carbonaceous matter, less than a quarter of an inch in thickness, from 

 which, up into another layer of pumice, projects the remains of the 

 branches of some small plant which had apparently been killed by the 

 overflow of the pumice. Lieut. Williamson gives a striking" view of this 

 locality, and speaks of it in the following terms: 



This river canon is very remarkable. Its sides vary from eight hundred to two thou- 

 sand feet in height. The river lias cut down its bed to this immense depth through 

 successive strata of basalt, with occasionally a deposit of infusorial marl and volcanic 

 tufa, which has sometimes hardened into a kind of conglomerate sandstone ten or 

 twenty feet in thickness, and of a white, grey, or reddish color. We followed down 

 this canon for about five miles, when a rocky spur cut off all further progress, and 

 compelled us to attempt the ascent. This with great difficulty we accomplished, and 

 found ourselves on a plain thinly dotted with sage bushes and clumps of grass. We 

 continued our course, and, after crossing the bed of a torrent of the rainy season, 

 came to a very small stream, called Psuc-see-quc by the Indians. It was sunk in a 

 canon about five hundred feet deep, cut through successive strata of basalt, infusorial 

 marl, tufas, and conglomerate sandstone like that found in the Mpto-ly-as canon (pp. 

 84,85). 



Another locality in which these remarkable deposits occur is on the 

 Pitt river; and Lieut. Williamson's description gives such a good idea 

 of the mode of their occurrence that I transcribe it, also, below: 



The banks of the Pitt river, both above and below the mouth of Canoe creek, are 

 partially formed by regularly stratified sedimentary deposits, the first seen since leav- 

 ing the valley of the Sacramento. They appear on both sides of Pitt river at intervals 

 for several miles, being in many places interrupted or covered by beds of trap. They 

 are, perhaps, best exposed in the canon formed by the passage of the river through 

 " Stoneman's ridge,"' the most conspicuous of the lines of upheaval which form what 

 is known as the lower canon of Pitt river. They here exhibit a thickness of about 

 fifty feet, but are considerably tilted up, and are covered by a thick bed of trap which 

 has been poured out over them. They exhibit narrow and parallel lines of deposition, 

 but are very homogeneous, and can hardly be said to form more than two distinct 

 beds. Of these, the upper is white, resembling very pure kaolin, derived from the 

 decomposition of crystalline feldspar. 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 traps, porphyry, and basalt of all sizes, 

 from masses of two and even three feet in diameter, to pebbles. They arc 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 bv it, or, at least, 



