DETAILED GEOLOGY OF SILVER CITY RIDGE 



423 



posed of grains of pure quartz sand cemented with quartz with a variahle 

 proportion of chlorite in those portions which are of oreenish sliados. 

 Beds of the latter shades are generally finely laminated and originally 

 probably contained some argillaceous and ferruginous material. The 

 lamination is original, being due to conditions of sedimentation and not 

 to parallel development of minerals induced by tlie pressnre. 



The upper layer of the latan limestone at the point A is of the noi-mal 

 character and continues so to the point B. Just east of P> tlie cracks in 

 the limestone are filled with hard black chert, which within a distance of 



FicruK 



-The Siliei- Citij Anticline 



Elevations are based on an assumed elevation of 1,000 feet. The area within the heavy 

 line is underlain by the altered rocks 



a hundred or so feet to the east comj)letely takes the place of the lime- 

 stone, tlie cliange being g]-adua]. 'I'lie strata are well exposed, so that no 

 mistake of identity is ])ossil)le. The change is also accompanied l)y a 

 thickening of the l)ed, an inci-easing ])ercentage of impurity therein, and 

 the assumption of a greenish shade. Fossils are visible in the re]daced 

 rock. A thin-section made from the chert tilling the cracks in the lime- 

 stone shows nothing othei* than would be expected in such a rock. A 

 section from the equiAalent of the limestone east of B shows the develoj)- 

 ment of a considerable amount of chloi'itc. At (^ there is no ti-ace of the 

 limestone, but what appears to l)e its stratigraphic position is held l)y a 



