80 TllC American (,,ologist. February. 19C0 
mountains. This radical change m trend of the axes in so 
short ^ distance is a rather singuhi. feature of the structure of 
these ancient mountains. 
Folds. — ^The structural "elevation" above mentioned con- 
sists of two great anticlines with a deep narrow syncline be- 
tween. At the foot of the mountains on the southeast, the 
formation next the Jurassic diabase and black slates of the 
lower mountain country, is almost invariably a belt of serpen- 
tine. The basement crystalline or so-called "picrolyte" rises 
rapidly from under the serpentine to form the axis of the first 
anticline which rises high above the adjoining black slate coun- 
try. This "picrolyte" forms the summits of some of the high- 
est peaks, attaining an altitude of at least 7.500 feet. The 
amount of elevation of the strata in the axis of this anticline 
it at least 8,000 feet, and its width averages between four and 
six miles. 
Another line of "picrolyte" peaks to the northwest, marks 
the axis of the other anticline, which is in every respect similar 
to the first. Between the two anticlinal folds, the synclinal 
trough is occupied by serpentine, with diabase and other intru- 
sives in great masses along the axis. Toward the Sacramento 
valley, the depression of the strata in the trough is so great 
that portions of the Jurassic formations appear in it ; toward the 
southwest, beyond the main Trinity river, the svncline be- 
comes shallower, the bounding anticlines lower, and the whole 
elevated belt displays mainly serpentine (the granites are not 
here considered). 
On the northwest of the second anticline, the serpentine 
again appears, overlying the "picrolyte" and dipping steeply 
away from it. By the continued descent of the strata toward 
the axis of the great Scott's valley syncline, the schist series is 
brought in and this in turn gives way, along the northwestern 
base of the Sierra Costa range, to the Carboniferous terranes. 
The schists appear nowhere in the range except on the western 
slope of the second anticline, where they outcrop in a north- 
south belt several miles in width, extending from the Upper 
Cofifee creek district across the head of Swift creek, Salmon 
river and Stuart's Fork, and emerge from the range near 
Weaverville. The line indicated is the site of the greatest 
mineral belt of Trinity county. 
