

GEOLOGY OF THE COAST EANGES. 



17 



which have originated the complex of alternating elevations and depressions 

 making up the system of chains known as the Coast Ranges, have been 

 apparently sudden and sharp ; so that the result may be called a crushing 

 and breaking, rather than folding and uplifting. Hence the very great 

 difficulty, on the Californian edge of the Continent, in getting sections of the 

 formations exhibiting regularity of succession in the beds, and having there- 

 fore real stratigraphical value. Often, and especially in the central and 

 northern portions of the State, the rocks for long distances are so broken up 



m 



that a recognition of their real structural relations is entirely impossible. 



And, while there are certain regions where fossils are abundant, on the 

 whole the Coast Ranges are not well supplied with these most important 

 aids to stratigraphical research. The more recent members of the Tertiary 

 are occasionally quite fossiliferous ; but the older Tertiaries and the Cre- 

 taceous are, as a rule, almost destitute of the remains of either plants or 

 animals. 



There is another fact which helps explain the difficulty of co-ordinating 

 the Coast Range geology. It is this ; that the rocks have been very con- 

 siderably metamorphosed, over wide areas, and that the products of this 

 ttietamorphism are the same in groups of strata of quite different geological 

 age. These masses of metamorphosed rock are often extremely irregular 

 m outline, and we find extensive areas where the chemical changes have 

 been carried so far as to completely obliterate the lines of stratification, 

 although perhaps producing only a, very slight change in the character of 

 the material, but thus making the deciphering of the original position of the 

 beds extremely difficult. The whole subject of the mctamorphism of the 

 Coast Range rocks is one of extreme difficulty, and it offers a fine field for 

 investigation. Many hundred analyses and microscopic sections of the rocks 

 Would be required for this purpose ; but the results, if the work were done 

 by capable hands, would be of great interest, especially with reference to the 

 banner in which magnesia has been introduced into the silicious and silico- 

 argillaceous strata, leading to the formation of the serpentine masses which 

 play so important a part in Coast Range geology. # That portion of the 

 ^oast Mountains which extends north from Clear Lake, and which, as before 

 Mentioned, is yet almost a terra incognita, both geologically and geographi- 

 ca hy ? must be carefully worked over before we can clearly discriminate be- 



* 



fe o striking is the preponderance of magnesian compounds in a portion of the Coast Ranges near the 

 w Ulna, that it is familiarly known to the people as the " Magnesia Country." 



