256 The American Geologist. ApHi, 1904. 
to the Pit shales by inter-stratification showing that deposition 
of ordinary sediments began before the vulcanism ceased and . 
also making it evident that there is no time interval represented 
between the two formations. 
Because of the Pit shales being conformably overlain by 
abundantly fossiliferous Triassic limestone and also of their 
containing Triassic fossils in the valley of Pit river, they cer- 
tainly are Triassic in age. The Clear Creek volcanic series 
occurring immediately under and conformable to the Pit shales 
is evidently also Triassic. That it is not Carboniferous is prob- 
able from the way it unconformably overlies both Devonian and 
Carboniferous. Very late Carboniferous, if not even Permian, 
as professor J. P. Smith suggested to me, is represented in the 
Paleozoic belt east of the McCloud river and this entire Car- 
boniferous series, thousands of feet thick, must have been re- 
moved by erosion and the Middle Devonian rocks laid bare, 
before the first Clear Creek eruptions occurred. The non-con- 
formity here indicated is the -equivalent of that which in many 
places separates the Paleozoic from the Mesozoic rocks. 
I am aware that volcanic material including tufif seems to be 
present in the Carboniferous east of the McCloud river as at 
Grizzly peak, about eight miles north of the Big Bend of Pit 
river, to which locality I was directed by Mr. Diller. I am also 
aware that volcanic material including tuff occurs in the Trias- 
sic and Jurassic strata east of the McCloud river and higher 
stratigraphically than the lower portion of the Pit shales, but I 
discriminate between these other occurrences and the definite 
early Triassic series which I call the Clear Creek formation. 
The latter I always treat as a stratigraphic unit because in Trin- 
ity and Siskiyou counties where I study chiefly, it has definite 
structural relations similar to a sedimentary series. I will define 
the Clear Creek series as consisting of the entire mass of vol- 
canic material which, collectively considered, occurs in thick 
broad sheets unconformably overlying the Paleozoic rocks and 
passing conformably under the Pit shales. 
(To be Continued.) 
