nReCinNat OF GEOLOGY 
MAY-FUNE, 1909 
UPPER CARBONIFEROUS 
GEORGE H. GIRTY: 
VI 
The Upper Carboniferous, rather in contrast with the Lower, 
was a period of emergence of shores and of shallowed waters, and it 
presents the variety that appertains to such conditions. In con- 
sidering the stratigraphic relations of the Pennsylvanian and Permian 
one cannot fail to be struck by the local character of the phenomena, 
and the vast amount of detail, from which it is difficult to disengage 
facts of broader significance. One of the facts of larger moment 
is the general unconformity which occurs at the base of the Pennsyl- 
vanian rocks. The extent of the phenomenon may be gauged by this: 
that an unconformity probably occurs at this horizon all the way from 
Pennsylvania to the Mexican boundary, except possibly in the deeper 
troughs. The underlying strata range in age from pre-Cambrian 
to Upper Mississippian. This is evidently, therefore, an uncon- 
formity by overlap, but the overlap is sometimes not appreciable 
unless extensive areas be kept in view. Very rarely, I believe, is 
any angular unconformity to be observed, but there are basal con- 
glomerates and in many places unmistakable evidence of erosion 
in the subjacent strata. Some of the most noteworthy instances of 
erosion are to be found in Missouri where shales of Pennsylvania 
age were deposited in sink holes and subterranean channels in the 
t Read before Section E of the American Association for the Advancement of 
Science, at the Baltimore Meeting, December, 1908. 
Vol. XVII, No. 4 305 
