26 



GEOLOGY — CHICO CREEK TO FORT READING. 



still bare, and exhibiting all the waves and eddies of a flowing stream. Some of these trappean 

 rocks were apparently older. Among them were porphyry, trachyte, and volcanic breccia, in 

 which the imbedded fragments formed masses of several hundred pounds weight. No drift 

 action has modified the surface of these rocks ; but, with the exception of the marks of 

 atmospheric weathering, which they exhibit in different degrees, they are as rough, and their 

 surfaces as fresh, as though but recently formed. The thin soil which covers or surrounds them 

 is derived only from their decomposition, and is often highly colored by oxide of iron. It 

 seems to possess the inorganic elements of fertility, and sustains among the rocks a vigorous 

 growth of wild oat. 



On the north side of Bear creek valley is a more striking proof of the comparatively recent 

 date of volcanic action in this vicinity than even the lava streams. This is furnished by a vol- 

 canic cone 500 or 600 feet in height, which has a crater on the summit, and of which the sides 

 are covered with reddish scoria. 





VOLCANIC CONE NEAR FORT READTNC. 



On Bear creek black obsidian occurs in considerable quantities, and some of it was brought 

 me, as "probably some kind of xtone coal." 



The trap ranges in this vicinity, of which I have spoken, form high and sometimes preci- 

 pitous banks to the Sacramento river, with but little level land between them, and consti- 

 tute the entrance to the almost continuous canon through which it flows for nearly a hundred 

 miles. 



