Doc. No. 0.} 41 



9 



extent implied by the facts, except, perhaps, as a sudden rise of the land 

 from the ocean. 



" The formation of such lakes by an abrupt elevation in a region hav 

 ing the ranges of heights parallel with the coast, is certainly a possibility. 

 But the water to .make the alluvial accumulations, must be running- 

 water, and be in operation in its channels a long period. And how long 

 would, such lakes exist after an elevation? If the violence attending a 

 change of level did not open for them at once a passage, the accumula- : 

 tionof water during a single flood would break a passage through such 

 soft sandstone beds as occur at the mouth .-of the Sacramento." 



These terraces occur on the Sacramento to the distance of one hun 

 dred and fifty miles from the sea and at this point they wer^e^as high 

 above the level of t1Ke river as at any point lower dow^i, and have 

 nearly the same elevation in all parts examined above the 'existing level 

 of the stream. 



The flats are several miles in width, and until reaching Carquinez 

 Straits, no other place for a barrier could have existed. In this place a 

 permanent barrier of at least four hundred feet in height would have 

 been required, to set the water back so as to cover the upper terrace 

 one hundred and fifty miles above the mouth of the river, and in the 

 second place, the lake should have a surface slope like the present bed 

 of the river, for this is the fact with the land of the terrace of course 

 an impossibility. Wherever the bed of the stream was four hundred 

 feet above the level of the sea, there the terrace should disappear ; in 

 place of which they attain an altitude of seven hundred feet at the dis 

 tance of two hundred and twelve miles from the head of Suisun Bay.* 



It is therefore impossible that one or many lakes should accomplish 

 the results we have before us ; it is the proper effect of river floods, and 

 the terraces must be received as indicating a change of level in the 

 country. 



Was this change of level an abrupt one, or was it slow and gradual? 

 This seems at first, a question easily answered. We may best under 

 stand it by considering the changes that would take place during the 

 elevation of a region of alluvial flats. If a country rise abruptly, the 

 river will commence to work itself to a lower level, and proceed with 

 rapidity, ending finally the very gradual slope of ordinary rivers, hav 

 ing a descent of one or two feet per mile. At the same time, in the 

 season of floods the river would wear into the former alluvium (now its 

 banks) and widen its surface ; and this widening would go on at each 

 succeeding freshet till the river had a new lower plain on its borders. 



But Avould not the effect be the same during a gradual rise. As the 

 country rose slowly, the excavation of the livers bed, and latteral widen 

 ing during freshets would go on gradually with the same results, pro 

 ducing a deeper bed and a new lower flat, both of which would change 

 as the change of level progressed, and in case the lower flat resisted 

 removal in any part, the portion left standing would form a subordinate 



* I have in my possession at this time, specimens from this highest terrace, which is found 

 on Weaver Creek, Trinity County. They were taken from different depths of a shaft which 

 has been sunk through the alluvial deposit eight hundred feet ; the different strata found though 

 are composed of clay, gravel and sand, in nearly all of which, gold has been found through 

 out. 



6 



