254 The American Geologist. ^prii. i904- 
as the debris of the conglomerates. Instead, he finds abundant 
fragments of the shale and quartzyte in the soil and bestrewing 
the surface. Whenever I cross the line from the Paleozoic 
rocks to the Bragdon rocks I know it almost instantly by the 
sudden change in the surface debris. 
THE CLEAR CREEK VOLCANIC SERIES. 
As the Bragdon series in the eastern area is nearly every- 
where underlaid by a sheet of surface volcanic materials con- 
sisting of lavas, tuffs and dikes, it is necessary to discuss the 
latter at some length. Through information derived from Mr. 
Diller and also Mr. F. M. Anderson, supplemented by a little 
observation of my own, I am aware that these volcanic ma- 
terials were originally mainly andesyte and rhyolyte and are 
now altered to rocks abounding in sericite, chlorite and epidote, 
but for the purpose of this paper I will refer to their original 
rather than their present condition. 
The earlier eruptions appear to have been more basic in 
character than the later, so that the lower portion of the series 
was prevailingly andesitic in character, although it is possible 
that there may have been some basalts included. By alteration, 
these rocks have been nearly uniformly converted to a dull 
greenish color and I formerly termed them greenstone. This 
kind of rock constitutes the bulk of the series and where erosion 
has cut deeply into it, the greenstone may be the only rock left. 
That is the case generally in the western areas. The Clear 
Creek areas are traversed by narrow shear zones as are the 
Bragdon areas and in them the greenstone has been converted 
to a schist somewhat resembling the amphibolite schist of the 
Sierra Nevada region. But the greater portion of the series 
has suffered little or no dynamical metamorphism. There is, in 
consequence, little difficulty in distinguishing between those 
portions of the greenstone which were originally lavas (often 
vesicular) and those portions which were tuffs. I distinguish 
the tuffs from brecciated lava sheets by the heterogeneity of the 
fragments; compact and vesicular fragments of different vari- 
eties of lava being mixed together. The fragmentals are fre- 
quently coarse and in thick layers alternating with compact 
greenstone, vesicular in places. In addition to these very evi- 
dent lava sheets and tuff layers, there are more coarsely crystal- 
line portions of the formation which I suspect to have been 
