The Geology of the Coast Banr/es. — Lnirson. 349 
These cherts are in many cases true jaspers, but in others 
the silica is chiefly amorphous though of the same excessively 
hard, and flinty character. There are all gradations between 
the amorphous and the holocrystalline varieties and the transi- 
tion is thought to represent a passage in time from an origi- 
nally amorphous condition to the holocrystalline condition. 
In some few cases they pass into softer, earthy facies when 
the red pigment preponderates, and in other cases they pass 
locally into a quartz-rock resembling vein quartz. The Radi- 
olaria in these cherts are apparent to the ordinary inspection, 
with the aid of a lens, as minute dots which are quite dis- 
crete from the matrix in which they are imbedded. Are these 
radiolarian cherts deep sea deposits? Are they wholly of 
organic origin? What is the explanation of their remarkable 
bedding? What was the rate of their accumulation? The 
suggestion that the}'^ are deep sea deposits is negatived b}'^ 
their interbedding with sandstones. The occurence of sharply 
discrete casts of radiolarian tests in a dense siliceous matrix 
which usuallji shows no evidence of being made up of organic 
debris casts doubt upon the supposition that the whole rock 
may be of organic origin. The sporadic occurrence of the 
cherts in this particular field at different stratigraphic hori- 
zons and throughout the Coast ranges generally also militates 
against the organic hypothesis. If the cherts are wholly 
organic they would have formed continuous sheets of great 
extent. They do not. They occur in the form of innumer- 
able isolated areas, and the isolation cannot be ascribed to 
erosion. It is original. The silica of the cherts seems to 
have been originally an amorphous chemical precipitate, de- 
posited at local centers on the sea bottom, in which radi- 
olarian remains were sporadically entombed. Occasionall}' 
the silica is thickly charged with this debris. Usually it is 
not. The change which has taken place in the silica seems 
essentially to have been due to gradual crystallization analo- 
gous to the process of devitrification in glass, which change 
seems not to have atrected the forms of the radiolarian remains. 
The most probable origin of the bulk of the silica of these 
cherts seems to the writer to have been sub-marine siliceous 
springs of solfataric character. This '"crenitic" hypothesis 
offers a satisfactory explanation of the exceedingly irregular 
