158 Th C Linerican Geolog ist. March, 1892" 
adjoining slates, but also by the complex series of granitic por- 
phyry dikes extending into them often for several miles. 
In the southwestern part of Shasta county at Horsetown and on 
the Cottonwood creek occur the most northerly outcrops of the 
Horsetown beds, the upper division of the Shasta group. The 
lower division of this group, the Knoxville, or Neocomian, is. 
that which has been confounded with the metamorphics. The 
Horsetown beds are totally unaltered and but slightly disturbed, 
dipping eastward from 15°-35°. They rest unconformably on 
granite and the metamorphic rocks. 
The granite mass of the Trinity mountains terminates abruptly 
on the south, being cut off by a body of massive serpentine: 
which forms the summit of Bully Choop; one of the highest 
peaks of the Coast Range. Directly south of the serpentine, 
along the crest of the range, we encounter green talcose and 
chloritic schists in which the silicification, characteristic of the 
Coast Range metamorphics, is well developed. The schists are 
somewhat crumpled with the appearance of minute veins and 
bunches of quartz which follow the cleavage planes in an irregu- 
lar manner. These rocks are penetrated for several miles by 
porphyritic dikes, evidently offshoots of the granite on the 
north. This is positive proof that their period of upheaval 
dates back to the extrusion of the granite. These schists. 
extend southwest along the summit into Tehama county. 
To the west and north in Trinity county there is a repetition of 
rocks somewhat similar but more quartzose. On the eastern 
slope are argillaceous schists, quartzites, and small areas of 
limestone, overlaid in places to a hight of twenty-five hundred 
feet by shales, sandstones, and conglomerates of the Horsetown 
period. 
As the range is followed south along the western border of 
Tehama county it is found to maintain an elevation of over five 
thousand feet, while silification becomes more and more a char- 
acteristic of the metamorphism. Red jasper, a remarkably wide 
spread rock in the Coast Ranges, was observed first in southeastern 
Trinity county. 
The unaltered shales and sandstones of the Shasta group be- 
come very prominent in Tehama county; having a width of over 
twelve miles. They dip eastward at an angle of from 30°-45°, 
sometimes becoming nearly vertical near their western boundary. 
