80 
Kirtley F. Mather 
Appalachian trough where the plant remains indicate deposi- 
tion during earlier Pottsville times the latter was the case. 
In Ohio the Mercer limestone occurs not far above the Mis- 
sissippian-Pennsylvanian unconformity but the Sharon coal 
which underlies it has been referred to the Upper Pottsville on 
the evidence of the associated flora so that the oldest Pennsyl- 
vanian beds in this region are younger than the Morrow. The 
fauna of the Mercer has been described by Miss Mark.^® It con- 
tains seventy-two species, over half of which are pelecypods, and 
includes seventeen of the species which have been described from 
the Morrow, in addition to a half dozen other forms closely 
related to certain of the Morrow species. These seventeen are 
among those forms noted in the preceding section as ranging 
upwards well towards the top of the Pennsylvanian system. The 
Mercer fauna is essentially a molluscan one with few brachiopods 
and fewer bryozoans. It contains nothing suggestive of the 
Mississippian faunas, or a transition therefrom, and is evidently 
younger than the Morrow. 
The study of the faunal horizons of the Pennsylvanian of 
Kansas made by Beede and Rogers-^ affords the best informa- 
tion available at present as to the earlier Coal Measures faunules. 
Those authors divide the system as present in Kansas into ten 
stages lettered from A to J, grouped in four series. Included 
in the faunal list of four hundred Pennsylvanian forms which 
have been identified from that state are twenty-five of the Mor- 
row species. Most of them are shown to have a long range 
throughout the various stages. Ten are present in the Cherokee 
shales. Stage A, Series I ; the same number are introduced in 
the overlying Ft. Scott limestone at the base of Stage B, Series I. 
The remaining five are all present before the top of the Drum 
limestone. Stage D, Series II, is attained. A comparison of the 
fauna of the Cherokee shale with that of the Morrow group 
makes it clear that the former is much younger than the latter 
as it, like the Mercer, contains nothing suggestive of a transition 
from the Mississippian. 
In western North America conditions are much more favor- 
able for finding the record of a marine fauna contemporaneous 
with the Morrow, for in that region deposition not only began 
much earlier than in the northern and eastern Mississippi valley 
