THE INFUSORIAL DEPOSITS. 221 
the Des Chutes River, which were obtained from a deposit of great thick- 
ness, associated with volcanic rocks and found to be very rich in organic 
forms. The frequent occurrence of infusoria in connection with volcanic 
overflows and formation of various kinds — as, for instance, in the moya or 
volcanic mud of the Andes — had already excited considerable attention, and 
there was not a little discussion as to the meaning of this, at first sight, 
seemingly strange association. The attention of Ehrenberg, which had been 
repeatedly called to this remarkable association by specimens sent from 
various parts of the world, was especially aroused by an extensive collection 
of material furnished by Castillo from Mexico. These were chiefly obtained 
by means of Artesian borings, which had been executed in and about the 
city of Mexico. The results of the investigation of this material were pub- 
lished in the Memoirs of the Berlin Academy.* 
The examination by the California Geological Survey of various portions 
of the Pacific coast from Mexico to British Columbia brought together a con- 
siderable number of facts and a good deal of material from various localities 
of infusorial rocks. Those specimens collected which seemed from their ap- 
pearance likely to contain microscopic organic forms underwent a prelimi- 
nary examination at the hands of Professor Brewer and the writer, but most 
of them were forwarded to Mr. A. M. Edwards, at that time residing in New 
York and professing to make a special study of this class of subjects. Several 
years having elapsed without any report having been received from him, a 
duplicate series was sent to Ehrenberg, — this was in 1870, — and by the aid 
of this series and the specimens sent by the Fortieth Parallel Survey he was 
placed in a position to acquire a quite thorough knowledge of the organic 
forms enclosed in these deposits. 
The writer of this volume, perceiving that the nature of the connection 
between the volcanic formations and the infusorial strata which they enclose 
had not been fully comprehended, published an article on this subject in 
1867.+ This article was in considerable part translated and made the basis 
of a communication by Ehrenberg in the Memoirs of the Berlin Academy, 
* Under the title of “ Ueber miachtige Gebirgs-Schichten vorherrschend aus mikroskopischen Bacilla- 
rien bestehend, unter und bei der Stadt Mexiko.” Abhandlungen der phys. Klasse der Konigl. Akade- 
mie der Wissenschaften, 1869. 
t On the Fresh Water Infusorial Deposits of the Pacific Coast, and their Connection with the Volcanic 
Rocks. Proceedings of the California Academy of Science, Vol. III. p. 319. 
{ Abhandlungen der Konig] Akademie der Wissenschaften, 1870. The title of the communication is 
“ Ueber die wachsende Kenntniss des unsichtbaren Lebens als felsbildende Bacillarien in Californien.” 
