26 The American Geologist. July, 1894 
The geological structure of the central and north central 
portions of the county, lying immediately west of the lava, is 
comparatively simple. In the regularity of strike and dip of 
the strata over considerable areas it more resembles that of 
the Sierra Nevada than the Coast ranges. Eruptives too are 
of rare occurrence in the north central portion, that region 
lying between Kosk's creek and the upper Sacramento. While 
so much of Shasta county is auriferous, there is hardly a trace 
of the precious metals in this region. The metamorphic se- 
ries consists to a great extent of slates. Toward the western 
side of the county in the direction of the higher ranges of the 
Klamath mountains there is a considerable change in the 
character of the sedimentary rocks. Although there are large 
areas of slate, yet fine silicious conglomerates are very promi- 
nently developed. The strike and dip also become very ir- 
regular because of the many large masses of intrusive rock. 
It was in Shasta county that the Carboniferous was first rec- 
ognized in California. Dr. Trask made a considerable collec- 
tion from the Gray or Marble mountains near the mouth of 
the McCloud in 1854. Later work was carried on by Whit- 
ney's survey, but no important addition was made to our 
knowledge of the metamorphic series. 
In 1883 J. S. Diller. of the U. S. Geological Survey, began 
work in this section of California, making collections from 
several new localities of Carboniferous limestones. In 1890, 
with more complete paleontological material, the limestones 
on Cedar creek were determined as Trias. In the summer of 
1891 the writer found the first Jurassic fossils in place in the 
Big Bend region, although Mr. Diller had previously picked 
up float specimens near Kosk's creek. 
Jurassic of Big Cafion. The youngest portion of this series 
of metamorphic rocks is found just west of the lava sheet, 
whose western border in the northern part of the county is 
Kosk's creek and Pitt river. Big Canon enters the canon of 
Pitt river a few miles below Big Bend, and in this canon the 
first Jurassic fossils were found in place. The slates and 
shales vary from black to reddish brown in color, closely re- 
sembling the Jura of Taylorsville. The fossils were not abun- 
dant and consisted almost wholly of lamellibranchs. They 
were found in place and in float boulders in the creek bed. 
