————————————— ele 
GEOLOGY OF THE COAST RANGES. 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 
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 
metamorphism are the same in groups of strata of quite different geological 
age. These masses of metamorphosed rock are often extremely irregular 
in 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 metamorphism 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 
manner 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 
Coast Mountains which extends north from Clear Lake, and which, as before 
mentioned, is yet almost a terra incognita, both geologically and geographt. 
cally, must be carefully worked over before we can clearly discriminate be- 
* So striking is the preponderance of magnesian compounds in a portion of the Coast Ranges near the 
New Idria, that it is familiarly known to the people as the “ Magnesia Country.” 
