266 0. C. Marsh — Discovery of a Fossil Forest 



somewliat formal description of the process of tlieir produc- 



December, 1870. 



Since sending the above to press I have subjected plates, 

 coated with " sensitized " collodion to the action of the magnetic 

 field. I had hopes of thus obtaining a physical impress on tk 

 plate which would appear on flowing the " developer." Sensi- 

 tized films on glass and on iron plates were placed over and 

 between the poles of an electro-magnet with cores 1-7 in. in di- 

 ameter. Some plates were developed after removal from the 

 mag-net, others while under the magnetic action,— with and 

 without the light having acted upon them— but no trace of ef- 

 fect has been detected, 



I had also imagined that the magnet's action should have 

 placed the afl&nities in a more unstable condition, so that the 

 film would rise in sensitiveness after exposure in the magnetic 

 field ; but this, also, I could not detect ; nevertheless, I have 

 not given up the supposition that some action will be evolved 

 when more appropriate films, far higher magnetic action and 

 more delicate measures of actinic effect are used. 



February 13, 1871. 



During the visit of the ^ 

 Pacific Coast, in October last, £ 



tion, including the writer, whiL ^.. ^ — - •■-■j , , v. , 

 Cisco to the " Geysers," took occasion to examine a locan . , ' 

 few miles from the route, where a number of fossil trunKb 



Aet. XyL-KlX.- Notice of a Fossil Forest in Hie Tertiary of 

 California; by Professor 0. C. Marsh, of Yale College. 



Yale College Scientific party to the 

 ist, several members of the expec i- 

 while on their way from ^an m^'^ 

 )k occasion to examine a locality ' 

 ..... ...... .... .V,..., where a number of fossil trunks ot 



trees had recently been discovered. This point proved to oe ^ 

 much scientific interest, and, since it has received as yet app ^ 

 ently little or no attention from geologists, it may be we 

 note the more important results of our investigation. 



The locality is situated on a high rocky ^^f^J^^^^oi 

 county, California, about five miles southwest of ^^;^%"'2r^„nt 

 Springs, and perhaps ten miles south of the summit oim 

 St. Helena. The existence at this place of several pexx ^^ 

 trunks of trees was first made public by Charies n. v^ ^^^^^ 

 Esq., of San Francisco, who visited the spot m July la^^^ ^^^ 

 soon after, gave a short account of the discovery m ^ ^^^ 

 Francisco Bulletin. Our party was especially i»^^^^^^„„^in2 

 Denison for information on the subject, and for accomp . .^|^ 

 us to the locality during our first visit The ndge on w^^^ 

 the fossil trees were found belongs to the Coast ^^f u,,,. 

 and fonns the divide between the Napa and Santa «osd 



