24 



University of California. 



[Vol. i. 



heavy deposits in these rocks. The density of the rock is 2.018. 

 The ultimate source of the carbon compound, the presence of which 

 is revealed by these simple tests, was doubtless the bodies of the 

 minute animals whose shells have been removed by leaching. 



The fact that the moulds of the minute univalves are very sharply 

 defined and quite empty of mineral matter, indicates that these opal- 

 ine beds are original formations and not secondary silicifications. 

 There are gradations from the distinctly opaline varieties to the 

 chalky. Near the base of the series at the town of Monterey, there 

 are some sandstones. There are also occasional lenses of a dense 

 yellowish to mauve-colored fossiliferous limestone, and in the first 

 ravine east of the main coast road on the north side of the Carmelo 

 River, there are some beds which are both calcareous and gritty. 

 These beds are usually more or less of a rusty yellow color and 

 they are usually fossiliferous. Certain beds, also, in the vicinity of 

 Monterey are so rich in minute siliceous organisms that they have 

 been described frequently as beds of infusorial earth. 



Origin of the White Sliale. — The white shale of the Monterey 

 series is certainly a very remarkable and unique sedimentary for- 

 mation. It is certainly over 1,000 feet in thickness at Carmelo Bay, 

 richly fossiliferous, and is neither a sandstone, a limestone, nor an 

 argillite except as regards a very small percentage of the total volume. 

 Infusorial remains are abundant in certain portions of the series, and 

 their discovery, taken together with the soft chalky character of the 

 formation, has led to the belief entertained by earlier observers that 

 the entire series is of organic origin, and is made up of the siliceous 

 remains of diatoms, radiolaria, sponges, etc., etc. Such a concep- 

 tion of the origin of the series, taken with its great thickness, 

 would of course imply an enormous time for its accumulation. 

 This conception is, however, probably only partially true, as our 

 studies have shown. A microscopic examination of a large number 

 of specimens taken from many different localities reveals the fact that 

 the rock usually contains no microscopic organic remains other than 

 those which are calcareous and which dissolve with brisk efferves- 

 cence in very dilute acid on the stage of the microscope. Even 

 these calcareous forms are very scarce, having for the most part been 

 leached out as above indicated, and so giving rise to a porous struc- 



