60 QUICKSILVER DEPOSITS OP THE PACIFIC SLOPE. 



older sandstones, bat is not unknown among the Miocene beds ; and of 

 course where induration exists the tawny color due to oxidation penetrates 

 to a much smaller depth tlian in the rocks of looser texture. Deep brown, 

 highly ferruginous sandstone is frequent in the form of nodules, as are sin- 

 gle narrow beds, particularly in the rocks of the Chico-Tejon group, but it 

 seldom or never occurs in large masses. The sandstones of the Knoxville 

 (Neocomian) group are in great part metamorphosed, and they give rise to 

 the series of rocks which will be discussed in the following pages. The 

 unaltered Knoxville sandstones, on the other liand, lithologically considered, 

 do not materially differ from those of subsequent periods. This fact is not 

 a source of confusion in field work, however, for the portion of the Knox- 

 ville sandstones which has entirely escaped alteration is small, and, so fiir 

 as observed, these are associated with greatly disturbed and intensely met- 

 amorphosed rocks of the same period in such a way as to leave no doubt 

 as to their age when once it is established, as will be done In a succeeding 

 chapter, that the great epoch of upheaval and of metamorphism in the Coast 

 Ranges preceded the Chico and Wallala periods. There is more difficulty in 

 distinguishing the somewhat altered rocks of later periods from similar sand- 

 stones of the Knoxville group, but associated silicification and serpentiniza- 

 tion appear to be confined to beds not younger than the Knoxville series. 



Among the unaltered rocks impure limestones play an extremely sub- 

 ordinate but still important part, since they contain the best fossils of the 

 Knoxville group. More widespread are shales (sometimes calcareous), 

 which form a connecting link between the sandstones with a caleitic cement 

 and the limestones. The shales and limestones together form but a small 

 portion of the entire mass. 



Origin of the sandstone. — It is fouud that tho Unaltered or very slightly al- 

 tered sandstones of all ages may be discussed together from a lithological 

 point of view. The first point which suggests itself for consideration is the 

 internal evidence of their origin which these rocks present. One of the 

 more important generalizations resulting from the field study of the quick- 

 silver belt is that granite probably underlies the entire area of the Coast 

 Ranges. This inference has received unexpectedly strong confirmation 

 from the microscopical study of the sandstones, for the entire series is thus 



