TLIOCENE DEPOSITS. 241 



area the erosion has been hirgely controlled by the stratification, and the 

 resulting hills show straight slopes on one side parallel to the stratification 

 and abrnpt declivities on the other where the strata have been broken 

 through. As seen from the Grizzly Canon road about two miles south of 

 the north fork of Cache creek, a succession of such hills iTiight be taken 

 for a series of monoclinal uplifts. Near the stream the Cache Lake strata 

 have also been extensively terraced. But, while the erosion of these beds 

 has been considerable, when their prevalent earthy character and exposed 

 position are taken into consideration it is clear that, geologically speaking, 

 they must be comparatively recent, since otherwise they would long ago 

 have been washed entirely away. 



On and near the north fork of Cache Creek the lake beds are covered 

 unconformabl}' by a deposit of gravel usually 50 feet or less in thickness. 

 This is somewhat obscurely stratified, unconsolidated, and has been tilted, 

 though less than the underlying lake beds. It presents no strata in which 

 there would be any hope of finding fossils and its origin is not certain. It 

 ma}' possibl}' represent the very last stages of Cache Lake, oi', as seems to 

 me more probable, the earliest river deposits after the close of the Cache 

 Lake epoch. 



The lake beds can best be studied in the eastern corner of the area 

 mapped, for in the volcanic areas near Lower Lake the strata have been 

 considerably altered. Especially is this the case near the andesite, which 

 lies upon the Cache Lake beds conformably and has produced a decidedly 

 metamorphic influence upon them. This consists in depositions of calca- 

 reous matter, silica, and ferric hydrates, apparently through the action of 

 hot springs or of water heated by contact with the volcanic rock, rather 

 than b}- the direct influence of the heat of the lava. Similar results are 

 noticeable where the basalt has come in contact with the lake beds; for ex- 

 ample, near the lime kilns, northeast of Burns Valley. Tbe metamorphosed 

 lake deposits }"ield a red ooil full of white masses of calcareous rock, which 

 is said to be extremely fertile. 



Relation of Cache Lake to Clear Lake. As may be SCen frOUl thc UUlp, CacllC Lake 



overlapped the area at present occupied by Clear Lake, while, as h:is been 

 pointed out, the identity of the shells in the two and other circumstances 

 MON xiii IG 



