Gold-Beariug Lodes in California. — Hcrshey. 79 
ing in curious contorted folia of crystalline limestone, even in- 
creasing to one- and two-foot layers of impure marble. This 
hornblende schist contains more lime and less quartz, than 
the mica schist. It represents the same degree of dynamo- 
metamorphism as the latter. Indeed, I believe the entire 
schist series to be of practically the same age, relative to the 
other formations, and to have had the same subsequent history. 
A slight difference in the constitution of the upper and lower 
portions of the original sedimentary (shales and shaly sand- 
stones) caused the present observed difference in the results 
of the metamorphic action. 
The schist series here described is older than the Carboni- 
ferous black schistose slate of the Scott's valley area, and prob- 
ably represents a portion of the Silurian period of geologic 
time. 
Struchirc. 
Upon a hasty reconnoisance the structure of the Sierra 
Costa mountains appears extremely complicated ; but a more 
thorough study will demonstrate that, as compared with the 
same formations in the Sierra Nevada region, these mountains 
are constructed on a simple plan. Broadly generalizing, they 
consist of a broad structural elevation or "plateau," occurring 
on the southeast and occupying two-thirds of the area of the 
range, with a short, almost precipitous descent on the south- 
east, and a long slope on the southwest to the axis of a great 
syncline occupied by the Carboniferous schistose slates of the 
Scott's valley region. The strata everywhere dip at a high 
angle, often being nearly or quite vertical, and outcrop in long 
narrow belts of comparative regularity, parallel to the axes of 
the folds and approximately so to the planes of the major 
faults. 
From the Sacramento valley to that of the main Trinitx' 
river the strike of the strata and the trend of the axes of the 
folds is east-northeast to west-southwest. Then they bend 
round to nearly westerly, which is maintained only for a few 
miles, when there is a rather sharp change to a nearly due 
north-south direction; farther soulli, toward W'eaverville and 
Junction City, this changes to a soutlieasterly course, in con- 
formity with the general northwest-southeast strike of the 
strata in the countrv south and southwest of the Sierra Costa 
