Chemung and Catshill,— Stevenson. 51 
tion of the Pocono in Crawford county shows an unexpected re- 
lation to the Devonian,* for at about 200 feet below the Shenango 
sandstone, there is a persistent limestone, which, though non- 
fossiliferous in Crawford, carries many fossils in Warren and 
Venango counties. It is found also in McKean. The fossils 
from Warren and Venango have not been studied, but Prof. 
White says that one of the spirifers suggests SN. disjuncta. 
Chemung forms occur at the base of the Corry sandstone, which 
Prof. White thought to be the equivalent of the Berea grit of Ohio. 
In McKean county? Prof. Hicks found Chemung forms passing 
up into the Mauch Chunk or upper division of the Lower Car- 
boniferous and associated there as well as in lower beds with 
‘Waverly forms’, seven Chemung species having been found 
with seven determined and eleven undetermined species, regarded 
by him as of ‘‘Waverly type.” Prof. H. 8. Williamst has shown, 
in his discussion of the fossil faunas of the Upper Devonian, that, 
at some localities in southwestern New York and northwestern 
Pennsylvania, species belonging to the Chemung fauna lingered 
even into the shales underlying the Olean conglomerate, which is 
the floor of the Coal Measures. — It is sufficiently clear that, while 
the passage from Devonian to Carboniferous along the eastern 
outcrop and for many miles west and northwest from it, was 
marked by great physical changes, no serious disturbance oc- 
curred in the region of northwestern Pennsylvania and the ad- 
joining portions of New York and Ohio, where the passage was 
so gradual as to permit the Chemung fauna to overlap that of the 
Lower Carboniferous. But the fact that, at some locality or in 
even a somewhat considerable area, the passage from Chemung to 
Carboniferous is not marked by abrupt change in sedimentation 
and by a sharp limitation of faunas is not a good reason for em- 
bracing Chemung in Carboniferous. Other portions of the Ap- 
palachian region might be selected which would afford material 
for very different generalizations. 
If local continuity of sedimentation is to be accepted as of 
itself a good basis for grouping rocks into ages, one would be 
compelled, within a considerable area of Virginia, to inelude in 
*Geology of Crawford and Erie counties, p.88. | 
tL. E. Hicks in Report on Geology of McKean County, etc. pp. 30-31. 
fH. 8S. Williams; Bulletin of the United States Geological Survey, No. 
41. Chapter tv. 
