B. Silliman on the Grass Valley District. 237 
the district, slaty rocks occur, more or less talcose or chloritic in 
er; masses of serpentine also abound, forming at times 
one wall of the quartz veins. This serpentine is Pipers. met- 
amorphic of the magnesian rocks last named. The red soil, 
seen almost everywhere in the Grass Valley district, has its 
origin in the peroxydation of the iron contained in the green- 
stones and diorites, and set at liberty by their decomposition. 
The line of contact between the gold-bearing and metamor- 
phic rocks of Grass Valley, and the granites of the Sierra Ne- 
vada is met on the road to the town of Nevada, about half a mile 
before coming to Deer creek. The talcose and chloritic slates 
are seen to the north, in the direction of the Peck lode, and in 
the slate districts of Deer creek. Tet. 
The dip and strike of the rocks in the Grass Valley region is 
seen to vary greatly in different parts of the district. Follow- 
ing the course of Wolf creek, a tributary of Bear river, it will 
be observed that the valley of this stream—which is Grass Val- 
€y—as well as of its principal branches, follows in the main the 
line or strike of the rocks. Inthe absence of an accurate map 
of the region, it may not be easy to make this statement evident. 
But all who are familiar with the chief mines of this district, 
Will recall the fact, that the course of the veins in the Forest 
Springs location, at the southern extremity of-the district, is 
nearly north and south—N. about 20° E.—with a very flat dip to 
Will, if explored in depth, be found “in basin.” e dip at 
Lone dak ia alg 30° Y. at Allison Ranch it is about ao: W. 
sharp turn to the left, nearly at a right angle, and then resumes 
~ ormer course with 
where it strikes the Forest Springs locations, we find the Noram- 
‘a inclosed in syenitic rocks, dipping at _ — — 
a 10 the east, a dip seen also at still less angle 
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