64 



At'the depth of forty-three feet from the surface, a bed of marine shells was 

 found in fine gravel and sand, cemented by iron, giving the mass a considerable de 

 gree of firmness. Below the first fossil bed there were alternating beds of sand and 

 gravel, in which were imbedded the teeth of sharks and other portions of the skele 

 tons of fishes ; commingled with these were the remains of mollusca in large quan 

 tities, and of various species. From the specimens obtained, it appears very cer 

 tain that these beds were deposited upon the granitic rocks direct, as the fossil 

 specimens in the State collection will abundantly prove, for in these the fossil may 

 be seen adhering firmly to that rock. 



Above this heavy bed of drift, and at the distance of half a mile to the south, 

 the conglomerates crop out and form the summit of a high table ridge, on exami 

 ning which, the marks of the old water line of the sea were distinctly engraved 

 upon its surface for a linear disiance of nearly three miles. These rocks extend 

 north and south from this point, forming the summits of a set of similar table 

 ridges, for a distance of 20 miles, beyond which they were not followed in this 

 State. 



The altitude of these marine beds above the level of the sea is less than 800 

 feet, and in three localities they were found to range between 900 and 1000 

 feet. I consider these as corresponding with equivalent beds at the distance of 

 150 miles farther north. In this section of the State we have another illustra 

 tion of those periodical elevations which form so conspicuous a feature in almost 

 every district which has been visited, and which will prove a constant attendant 

 of the traveler wherever he may wend his way. 



The most eastern limit at which these tertiaries have been met with, is upon a 

 line running north and south and cutting through Mormon Island on the south 

 branch of the American River. The fossils beds will be found in the immediate 

 vicinity of the following localities, viz : Texas Flat, Half Way House., Volca 

 no Ridge, and Mississippi Flats in the county of Placer. The conglomerates pn 

 these table ridges are the same as those which pass beneath the edge of the valley, 

 and it is in this section of the State, that the thickness of those rocks can be 

 ascertained with a precision, sufficiently accurate for any practical purpose. 



By reference to my notes taken at the beds, I find the following to be the order 

 and thickness of the deposits as they occur at the different localities above named, 

 and which are known to reach the edge of the plains immediately to the west. This 

 table includes the rocks only, and such as are known ' to pass beneath the eastern 

 border of the valley, and may serve to direct those operations which were spoken 

 of in the preceding article. 



THICKNESS OF THE SEDIMENTARY ROCKS IN THE SIERRA NEVADA. 



East of the border of the Valley. 



Argillaceous Slates, 



Conglomerates, 



Clay, sands and gravels, 



Total, 



At the border of the Valley. 



FEET 



Argillaceous Slates, 



Conglomerates, 270 



Sand, Clays, &c., 56 



Total, '- - 456 



