248 The American Geologist. ^p"1- i^*^^- 
THE BRAGDON FORMATION IN NORTH- 
WESTERN CALIFORNIA. 
By OSCA.R H. Hekshey, Berkeley, California. 
INTRODUCTION. 
When I first arrived in California, in 1897, I was supplied 
with a geological map of the United States, extracted from an 
Annual Report of the U. S. Geological Survey. On this map, 
certain areas in northwestern California were represented as 
Carboniferous and certain others as Jura-Trias. One of the 
latter included the territory in which I began to prospect and 
in this manner I derived my first intimation that the rocks of 
Trinity mountain are Mesozoic in age. 
I spent several months in the vicinity of Bragdon, in Trin- 
ity valley, and became somewhat familiar with the geological 
relations of the rocks of Trinity mountain. I learned that the 
contact between a certain volcanic series and an overlying black 
slate and quartzyte series is the principal gold "pocket" horizon 
of that territory and naturally I devoted a large portion of my 
time to the investigation of that contact. I panned up to it, I 
followed it continuously for miles and I dug along it repeated- 
ly. It has been suggested to me from time to time by geologists 
who have not given close attention to that contact that the vol- 
canic material lies under the slates because of intrusion, but all 
the phenomena I have ever been able to observe along that con-' 
tact indicate unmistakably that the Bragdon sediments were 
laid down upon the volcanic series. This position I have main- 
tained in a paper published in July, 1899, another in April, 
1901, and yet another in April, 1903.* 
As I extended my field of operations I found in Trinity 
county an entirely different slate series whose stratigraphic po- 
sition seemed under the volcanic series and I temporarily de- 
nominated it the "Lower Slate Series" to distinguish it from 
the "Upper Slate Series" or Bragdon formation. 
* "Origin and Age of Certain Gold 'Pocket' Deposits in Northern Califor- 
nia," Amer. Gkol., vol. xxiv, July, 1899. 
"Metamorpliic Formations of Northwestern California," Amkr. Geol., 
vol. xxvii. April, 1901. 
"Structure of the Southern Portion of the Klamath Mountains, California," 
Amkr. Geoi.., vol. xxxi, .\pril, 1903. 
