348 The American Geologist. June, 1904. 
creek, have cut down through the shales into the volcanic rocks. 
In several former papers, already referred to in this, I have 
described the system of folds which traverses this area. Trinity 
river traverses these folds transversely and across each arch 
has cut down beneath the shales. 
In some of these small isolated Clear Creek areas encoun- 
tered deep in the valleys within the Bragdon area, vesicular 
lavas and tuffs are present in unmistakable form. As a locality 
for the latter I will mention a point on the stage road about one 
mile south of Bragdon and for the former almost any green- 
stone outcrop near Bragdon. These outcrops are identical in 
character with outcrops along the Sacramento river near Cop- 
ley. Prospecting the contact shows that these tuffs and lavas 
pass under the shales all around these isolated areas. Similar 
.altered tuffs and lavas pass under the shales nearly all around 
the Bragdon area. I can see no escape from the conclusion that 
the Bragdon formation in this eastern area is nearly everywhere 
floored (with an important exception to be noticed later) by 
the volcanic series. 
The relation of the Bragdon to the Clear Creek formation is 
quite different from that of the Pit shales. I have never seen 
the least evidence of interstratification between the volcanic 
material and the Bragdon shales. The relation is one of non- 
conformity. The shales rest indiscriminately on different mem- 
bers of the lower series. By means of the inter-Bragdon vol- 
canic areas one may trace a belt arrangement of the volcanic 
phases similar to that near the Sacramento river. For instance, 
the stage road betvvcen French Gulch and Trinity Center 
crosses, in descending the western slope of Trinity mountain, 
a narrow belt of altered rhyolyte which has a direction appar- 
ently easterly and is bounderl by the ordinary altered andesyte. 
This altered rhyolyte penetrates deep into the volcanic series 
and is either a sheet standing on edge or a dike. It is cut off 
sharply by the base of the overlying shales and whether a tilt- 
ed sheet or a dike, much of il must have been removed by eros- 
ion before the shales were deposited. This altered rhyolyte 
belt shows that rhyolyte was developed this far west and its 
rather uncommon occurrence in Trinity county probably is due 
to its having been removed by erosion previous to the deposi- 
tion of the shales. 
