Doc. No. 9.] 31 







question, unless deeply seated, and entirely covered, edges and all, by 

 the sedimentary rocks above noticed^ 



The character of the soil in many parts of this valley will render it 

 of little importance as an agricultural district, unless water in ample 

 quantities for irrigation can be obtained. (These remarks apply partic 

 ularly to the upper terrace of the valley on each side of the river.) And 

 we hope that attention may be called to this very important subject of 

 making the extensive areas of the arid districts of the basin available 

 for market and agricultural purposes." 



Experience has demonstrated the almost certainty of obtaining water 

 and in sufficient quantities for agricultural and other purposes, in all val 

 leys resting upon sedimentary formations and having a basin-shaped 

 structure, and where the different beds have a degree of uniformity or 

 regularity in their position, and are of a texture that will admit the free 

 percolation of water through the superior beds and sufficiently firm to 

 prevent its escape in those below. 



These conditions are all fulfilled in the basin of the Sacramento, and 

 from the united testimony of different observers, we have ample evi 

 dence that the sedimentary formations of one side are the same as those 

 upon the other, with the exception, perhaps, of the conglomerate. 



The absence of the conglomerate on the west side of the basin, will 

 not affect the result of obtaining water by the means proposed. The 

 clays and clay-slate, below the sandstone, appear on both sides and are 

 sufficiently impervious and firm to prevent the escape of any water that 

 may rest upon them.*" 



EEYIEW OF THE GEOLOGICAL CHANGES IN THE COAST 

 MOUNTAINS AND MONTE DIABLO EANGE. 



Having briefly detailed the more general characteristics of the geology 

 of the above mountains, it will become necessary to review in a mea 

 sure the geological changes that have been instrumental in producing 

 the peculiar features noticed in the preceeding pages ; in doing this the 

 same lines will be followed as in the outset. 



Starting from the Straits of Carquinez, it has been stated that the 

 rocks forming the borders of those Straits and part of the adjoining 

 bays, were composed of a recent sandstone ; in following up these in a 

 southerly direction for a few miles, we find the sedimentary rocks thin- 

 ing out, and are succeeded by high hills and low mountains of volcanic 

 rocks, composed of trochytes and other intrusive rocks of recent date. 

 'These are followed by the primitive rocks, composed of the older trap, 

 in the vicinity of Oakland, consist in a great measure of serpen 

 tine. 



The latter rocks form the western side of this part of the 



* Since October last, there have been three Artesian borings, carried to depths within one 

 hundred feet, on the valley of Santa Clara, and in the vicinity of San Jose. The result of 

 each has been successful, and a head of water from four to nine feet has been obtained. 

 These indications of water so near the surface and in such quantities, will much enhance the 

 value ot agricultural land throughout this valley and render available much that would 

 otherwise have laid unocupied and unimproved for years. 



