454 QUICKSILVER DEPOSITS OF THE PACIFIC SLOPE. 



Sandstones often ocrur here in practically uninteri-upted series of beds 

 many thousands of feet in thickness. The unaltered sandstones of the 

 Coast Ranges are very much alike, whatever their age. The Tejon (Eocene) 

 beds, however, are of a much lighter color than the Chico (late Cretaceous) 

 or the Miocene rocks. The Chico again is usually more indurated than the 

 Pliocene. While the Knoxville (Neocomian) sandstones where unaltered 

 closely resemble those of later periods, no case is known in which unaltered 

 Knoxville beds are not intimately associated with greatly disturbed and 

 metamorphosed rocks of the same age, so that there is no difficulty in dis- 

 crimination when once it is established that the epoch of violent upheaval 

 and metamorphism followed soon after the close of the Knoxville. 



Field study showed that the Coast Ranges are probably everywhere 

 unaerlain by granite. The microscopical examinations have given this in- 

 ference unexpectedly strong confirmation, for, though on structural grounds 

 it appears cei'tain that a portion of the later sandstones were formed at the 

 expense of earlier arenaceous beds, they all exhibit unmistakable evidence 

 of granitic origin. They are thus so similar that they may be discussed 

 together lithologically. The microscope shows that the main constituents 

 are quartz fragments (containing abundant fluid inclusions and in other 

 respects resembling the quartzes of the underlying granite), orthoclase, the 

 same plagioclases found in the granite, and biotite. Most of the less impor- 

 tant constituents of the granite are also found in the sandstones. The pro- 

 portion of quartz in the sandstones is, as a matter of course, greater than in 

 the granite. The grains are conmionly rounded like ordinary beach sand, 

 but are sometimes extremely sharp. The cement is largely calcite. The 

 sandstones are subject to the ordinary decomposition known as weathering, 

 by which the ferromagnesian silicates are in part converted to chlorite and 

 in part to a ferruginous cement 



The iinmetamorphosed late Cretaceous and Miocene sandstones show 

 numerous concretions. These in rare instances contain fossils as nuclei. 

 A representative concretion in which no organic remains existed Avas inves- 

 tigated. It was found that the cementing matrix contained a considerable 

 amount of phosphoric acid, but was chiefly composed of a mixture of cal- 

 cium carbonate and a hydrous subsilicate of iron. It is shown that this 



