Califovnian Metamorphic luvniations. — Hcrshcy. 235 
the amphibolyte schist of the Sierra Nevada region. Bands of 
impregnation of sulphides are also commonly associated with 
these shear zones. 
Another modification of the diabase quite common along 
Trinity river is into a very hard, fine-grained, purplish flinty 
rock, perhaps due to silicification of the greenstone. In the same 
region occur dikes of quartz-porphyry which cut the green- 
stone but terminate abruptly at the base of the overlying slates. 
In fact, the whole greenstone formation appears to be a series 
of diabasic tufifs and lavas bound together by a varietv of in- 
trusive porphyries and diabase. 
This greenstone in large part is beyond doubt extrusive in 
character ; in other words, it is a formation of surface volcanic 
material. It has its counterpart in the Neocene tuffs and lavas 
spread widely over the older formations in the Cascade region. 
On the isthmus of Panama, I have studied a great Neocene 
volcanic formation of precisely the same character, except that 
the tuffs are mainly rhyolitic and the lavas basaltic. The in- 
ternal structure of these formations is characteristicallv alike. 
The origin of the material of the greenstone has not yet 
certainly been discovered. The Lower Slate series is particu- 
larly abundantly supplied with dikes of greenstone scarcely dis- 
tinguishable from the main body of the diabase and in places 
these intrusive diabases seem to pass into the extrusive forma- 
tion. In the Cinnabar synclinal between the gabbro ridges 
of northeastern Trinity county, great dikes of greenstone are 
intruded into the serpentine and form extensive bodies along 
the axis of the trough. The entire region from the Sacramento 
river southwestward to the Hay Fork country and northwest- 
ward to the lower Salmon river country appears to have been 
overspread by this greenstone, for wherever its proper horizon is 
-exposed, viz., between the Lower Slate series and the Bragdon 
slates, heavy bodies of diabase occur as a stratigraphic unit 
and not as intrusions. 
Tuffs imply volcanoes and not mere fissure eruption. The 
volcanoes of this period have disappeared, but I think they oc- 
curred along a belt lying just west of the Sacramento river and 
including the sites of, say, Kennett, Keswick, Shasta and Cen- 
terville. Here the formation is very thick and its fragmental 
character is most apparent. Toward the westward it appear.'; 
