66 
Kirtley F. Mather 
between the three faunules will at once come to mind. A study 
of the range of the different Morrow forms, as summarized in 
Table II, makes it quite clear that the life-assemblage of each 
of these horizons was distinct from that of the other two although 
the three have a common aspect. 
Doubtless the absence of certain of the more rare forms from 
a horizon is more apparent than real as it cannot be supposed 
that every form of life which composed a faunule has found a 
place in the collections upon which these studies are based. It 
is probably significant that eighteen of the twenty-two species 
which have been recorded as ranging throughout the entire Mor- 
row group are brachiopods, by far the most important numeric- 
ally of all the classes of life represented and hence the least 
likely to escape collection. On the other hand, the fact that only 
four species are known from the lower and higher horizons with- 
out also being recorded from the intermediate one would indi- 
cate that our knowledge of the faunules is not seriously incom- 
plete. 
Not only does the distinctive nature of the individual faunules 
appear from the statistical method of comparison but it is also 
clearly indicated by a comparison of the types of life present or 
absent as the case may be. For example, the genera, Pentre- 
mites and Archimedes, which are of a decided Mississippian 
aspect and are represented by forms which have lingered on 
into Pennsylvanian times, do not range above the Brentwood 
limestone, while certain of the typically Pennsylvanian types 
such as Campophyllum and Pseuclomonotis do not appear beneath 
that horizon. Meekella, Worthenia, and several other Pennsyl- 
vanian forms are not introduced until the deposition of the 
Kessler limestone. 
As has been pointed out on a preceding page, the character 
of the Morrow sediments changes notably toward the west and 
throughout most of the Oklahoma region the strata have been 
mapped as a single formation. Limestone is the dominant 
rather than the subordinate type of rock and the whole series 
thins markedly toward the west and northwest although the 
limestone is somewhat thicker than either of the limestone 
members of the Bloyd shale. The question suggests itself as 
to the exact relations of the western limestone to the limestones 
