Igneous Rocks of Rossland . — B. C. Barber. 347 
yte and vogesyte occur at the 200 foot and 400 foot levels of the 
Dorleska mine. Union creek, Trinity county, California. The 
lamprophyres of this locality contain considerable calcite and 
are badly weathered. 
These locations are the most notable occurrences of the 
lamprophyres in America ; the rocks have the same general 
composition as the Rossland rocks, but are all more or less 
weathered and decomposed, while the Rossland rocks are very 
notable for their great freshness and beauty of their sections. 
They were nearly all taken from several hundred feet under- 
ground, under conditions where lamprophyres have seldom been 
collected. 
Along with these are the hornblende dioryte and dioryte 
porphyry ; in general composition these are like the campton- 
ytes and kersantytes but lack the lamprophyric structure. 
The monzonytes and syenytes are light colored, acid and 
granular. Their intergradation, as shown by a study of thin 
sections and their apparent intergradation in the field suggest 
the probability that they are products of differentiation from 
the same parent magma. It was, however, not possible to de- 
termine from the data at hand whether the dioritic rocks were 
differentiated before the syenytes and monzonytes, although 
this seems probable. 
THE BRAGDON FORMATION IN NORTH- 
WESTERN CALIFORNIA. 
By Oscar H. Hershey, Berkeley, California. 
{Continued from April number, page 256.) 
THE STRUCTURE OF THE EASTERN BRAGUOX AREA. 
The Bragdon and Clear Creek formations occupy a broad, 
comparatively shallow, basin-shaped depression in the surface 
of the upturned and eroded Paleozoic rocks. This basin is lined 
by the volcanic series which is overlaid in the central portion by 
the shales, quartzytes and conglomerates. Originally the Brag- 
don formation completely covered the Clear Creek rocks, but it 
has been upturned around the borders, eroded and the volcanic 
series laid bare. At various places within the limits of the 
Bragdon area, the streams, such as Trinity river and Clear 
