300 The American Geologist. November, looi. 
the several provinces of the Carl)oniferoiis are, as yet, no- 
where carefully determined. Separating- the exposed areas 
are hroad stretches of country in which practically none of 
the younger Paleozoics are represented in outc'rop. Another 
consideration is the fact that the formational units established 
in the various districts, have been largely local in nature 
and tentative. They are now known to possess widely dif- 
ferent ta^xonomic values, hence permitting only very vague 
stratigraphical correlations to be carried on. A third feature 
is one which has been thought by many workers to render all 
attempts at paralleling horizons useless, and is the diversity 
of origins which the sediments jM'esent. The marine nature 
of the deposits in one province, as in the Rocky Mountain 
region for example, and the general presence of littoral con- 
ditions at the time the formations were laid down in other 
regions, as in the Appalachians, would seem to almost pre- 
clude comparison. 
In the Mississippi valley, however, there are all of the 
several kinds of conditions of sedimentation well represented. 
The marine deposits alternate with off-shore and coastal sed- 
iments. Not onlv do the dift'crent kinds of formations alter- 
nate, but many extensions of those from the west interlock 
with those from the east. During several distinct epochs the 
sea encroached upon the domains of the coastal deposits-. At 
other times the ccarse land-derived materials were carried 
far out into areas where more open-sea conditions had previ- 
ouslv prevailed. In the general vertical section of the Mis- 
sissippi valley, or more spec'ificallv that of the Ozark region, 
where is perhaps the best representation of strata, is believed 
to exist a record that in all respects sufficiently approaches 
both that of the East and that of the West, to enable it to be 
mlade useful in the exact Correlation of the serial relations of 
the Carboniferous of the wdiole country. The relations of this 
succession of formations is such that from it, it appears possi- 
ble to construct the schematic section of the Carboniferous 
for the entire American continent. 
The chief merit of the g-eneral Ozark section of the Car- 
boniferous as a standard of reference is its exceotional com- 
pleteness. No other section of the Carboniferous rocks on the 
Americtm continent possesses such an enormous thickness. 
