322 PROCEEDINGS OF THE CALIFORNIA 



deposits to be of eruptive origin, is evident from a remark in his last commu- 

 nication, (that in reference to the specimen from the Toluca Valley) to the 

 effect that the occurrence of fresh-water forms, exclusively, in these infusorial 

 masses is evidence that volcanic phenomena are not dependent on, or connected 

 with, the presence of sea-water, as is generally supposed, from the fact that vol- 

 canoes are situated, in most cases, near the sea coast. 



Not having the necessary works of reference at hand to be able to see, in all 

 the cases cited by Ehrenberg, exactly what the evidence is, on which his theory 

 of the origin of these infusorial deposits is founded, I will not attempt to give 

 an authoritative statement in regard to any others than those which belong to 

 this coast ; but I cannot avoid drawing the inference, that the same conditions 

 which are so easily traced here will, on future examination, be found existing in 

 all the other localities cited by him. 



The mode of occurrence of these fresh-water infusorial deposits in California, 

 and on the Pacific coast in general, is very simple. They are accumulations of 

 organisms which have been collected at the bottom of the lakes, or in the lake- 

 like shallow expansions of rivers, in which they grew. This growth took place 

 at a time when volcanic agencies were busily at work, giving rise to accumula- 

 tions of ashes, pumice, and other materials. The rapidity with which these in- 

 fusorial deposits form, at the present time even, the vast extent over which they 

 are distributed, and the general importance in the geological history of the 

 earth, are now matters which are well understood, of the masses thus accumulated 

 and in regard to which the store of facts has been rapidly growing in magnitude 

 during the past few years. The mud deposits and deltas of rivers, the bottoms 

 of lakes and swamps, and the bed of the ocean itself, are the repositories of 

 these forms. Heat and stagnant water seem to be what is required for their 

 rapid reproduction and the consequent rapid accumulation of their remains. 



The infusorial deposits of Central California— I refer now to those of fresh 



water origin, and connected with volcanic masses — are all situated in such 



positions as to show, that they were formed and deposited in shallow water ; 



that, through the various alternations of calm and convulsion in the Sierra, they 



were at one time allowed to accumulate in quiet, then swept over by masses of 



gravel and sand, indicating a furious rush of water, then covered with a shower 



of ashes and pumice from the neighboring volcanoes of the Sierra then in active 



operation ; and finally, at the grand finale of the basaltic lava overflow of the 



chain, capped with this indestructible material, which has effectually prevented 



the washiug away of the otherwise easily removed infusorial deposits. This is 



the connection between the volcanic and the infusorial masses ; by their absolute 



indestructibility the former have protected the latter from denudation, and 



consequently we see them always accompanying each other : for where the cover 



did not exist, there the denuding forces have swept away every vestige of the 



soft and easily yielding material, or else it remains concealed under the water. 



To form an idea of the extent of the erosion which has taken place since these 



infusorial beds were deposited, and the consequent change in the configuration 



of the country, we must bear in mind that the whole of the present river canons 



on the west slope of the Sierra have been excavated since that time, and that, in 



