Doc. No. 9.] 



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occurs, having a thickness of about one hundred feet ; these rocks com 

 port in position with the other sedimentary rocks above them, and are 

 found resting directly on the granite, and other igneous rocks far into 

 the interior ; in the lower hills their structure is fissile, cleaving with 

 ease over considerable surfaces, while in the eastern parts of the moun 

 tains they have often acquired a crystaliiie structure from contact with 

 other and more recent volcanic rocks, and such as have broken through 

 and disturbed the primitive formation. 



On the western side of the valley or basin, the series do not follow in 

 precisely the same order as occurs on the east ; the sandstone and slate 

 of the same age is found, but the conglomerate is wanting ; if it exists, 

 it is completely obscured from view, except on the west slope of the 

 coast mountains towards the sea, and its occurrence there is a reason for 

 the supposition that it does exist below the other stratified rocks on their 

 eastern slope. Above all the others, the miocene rocks are found dis 

 turbed and cut through by the recent volcanic intrusions of that period. 



The following then will be the arrangement of the rocks from below 

 upward : 



EAST OF THE SACRAMENTO RIVER, 



Primary Rocks. 



Sedimentary. 



I 



Granite. 



Slates. 



Conglomerate. 

 Slates. 

 Sandstone. 



WEST OF THE SACRAMENTO RIVER, 

 Primary Rocks. Granite. 



Slates. 



Uncertain. Conglomerate. 



Sedimentary. Sandstone, Eocene. 

 Sandstone Miocene. 

 Recent volcanic cuting the latter. 



"With this arrangement of the stratified rocks which pass under the 

 California Basin, it is obvious, that the waters flowing at the line of 

 junction between the sandstone and the slate-rocks below them, muss 

 pass under the sides and central parts of the valley, varying in depth at 

 the distance from either of its borders increases. 



It must be remembered that the dip of the sedimentary rocks on 

 which the alluvium of the valley reposes, will increase or diminish the 

 distance that may be necessary to bore for obtaining water, as the incli 

 nation of these rocks is greater or less ; and with the view to demonstrate 

 if possible, (or at least approximately) the depth that it might be neces 

 sary to sink in order to obtain a plentiful supply of water for agricul 

 ture or other purposes, an examination of both borders of the basin was 

 made of fifty miles in length, and the mean of all the dips taken. 



It was found by measurement that the surface of the basin rises at 

 the average rate of six feet per mile from the river to either of its bor 

 ders. Taking the grade of the surface with the lowest average dip of 

 the rocks where they pass under it, (being equal to twelve degrees,) and 

 assuming that the sedimentary rocks decrease in inclination, as the dis 

 tance increases, which is probably the case, it will be found necessary to 



