SKMICRYSTALLINE PORTION OF THE PRE-CRETACEOUS. 87 



where but little distortion and metamorphism have been felt, and the 

 argillaceous rocks still retain their soft, shaly character. 



The semicry stall hie Portion of the Series. — As we follow the pre-Cretaceous 

 series toward the north it gradually assumes a considerable degree of 

 metamorphism, both chemical and d3'namic. According to the reports 

 of various observers, the series forms the basal rocks exposed in Mendo- 

 cino, trumboldt and western Del Norte counties. The late W. A. Good- 

 year, for a number of years a member of the Geological Survey of Cali- 

 fornia, under Wiiitney, though considering these rocks as metamorphosed 

 Cretaceous, noted very distinctly the gradual increase of metamorphism 

 toward the higher portions of the northern Coast ranges. In view of the 

 utter lack of any attempt on his part to demonstrate a particular theor}^, 

 the following quotation has the highest significance : '^ 



"It appeiirs to be a remarkable fact, which I noticed not simply on this Eel 

 river trip, but also elsewhere in our travels, that as we approach the higher moun- 

 tainous regions northwest of Clear lake the general lithological character of the rocks 

 appears to undergo a gradual change. The country appears to be almost every- 

 where metamorphic, and, so far as I have seen, the degree of metamorphism is 

 often higher than otherwise, though in some places every stage may be found from 

 entirely unaltered to the most highly altered and crystalline rock, but the charac- 

 ter of the change is different. Tlie quantities of serpentine and of the jaspery and 

 semi-jaspery rocks of the Coast range farther southeast rapidly diminish, -while 

 micaceous and hornblendic schists and argillaceous slates, etcetera, are oftener 

 seen. In short, the rocks seem to belong to the classes which are generally more 

 crA'stalline in their texture. The quantity of lime in the rocks also appears to 

 diminish. White solid quartz occurs far more frequently. Even the granular 

 metamorphic sandstones have a different look. 



"At one point near Upper lake I noticed even the entirely uualtered sandstone 

 so filled with scales of mica as to render its structure thoroughly schistose. In- 

 deed, appearances everywhere are such as to suggest at once the question whether 

 on going northwest from Clear lake, among the higher mountains, there is not a 

 gradual and more or less complete change in the general lithologic character of the 

 rocks, from that which is peculiar to the Coast range farther southeast to one which 

 is more similar to that of the rocks on the western slope of the Sierra." 



The writer's field-work has extended along the crest and eastern slope 

 of the Coast ranges from Napa county north to Siskiyou county. The 

 gradual increase in metamorphism is very i)lainly to be seen, together 

 with a considerable change in the lithologic character of the rocks. Jas- 

 per, slate, hydromicaceous and chloritic schists occur in many ])laces on 

 the eastern slope of tlie Vallo Bally mountains, and, according to Mr 

 Goodyear, the rocks on the western sloi)e are much the same. The 

 summit of the range consists of an exceedingly contorted and silicified 



♦Tenth Report of State Mineralogist of California, p. .310. 

 ,\in-BuM,. CiKor,, Soc. Am.. Vol. G, 1804. 



