IOWA ACADEMY OF SCIENCES 
201 
While some of the species from the limestones also occur in the 
shales, they are represented usually by so few individuals that they may 
be considered in the latter as purely accidental occurrences. 
To the eastward the conditions of sedimentation are reversed. Shales 
predominate, with limestones intercalated. The shales are quite fossili- 
ferous. Forms from the shales only sparingly occur in the limestones. 
The faunas of the limestones are very distinct from those of the shales, 
but among themselves are practically the same. Moreover, they are es- 
sentially identical with those from the limestones higher up in the Mis- 
sourian series of Kansas. 
Kansas shales have not been exhaustively examined for fossils. 
Those shale formations of the Missourian series which have been care- 
fully examined carry the typical forms of the shales of the lower Des 
Moines and Arkansan series rather than the types of the Missourian 
faunas as generally known, which is the limestone fauna. 
There is, then, in the Coal Measures of Iowa, Missouri, and Kansas 
an alternation of faunas corresponding to the alternation of lithologic 
units. There is a characteristic fauna of the limestone formations; and 
there is a characteristic fauna and a flora of the shale formations. The 
main reasons why the two faunas have not been differentiated are these; 
Little attention has been paid to the formational range of the organic 
remains. Comparative abundance of the invertebrates in each forma- 
tion has not been noted. The tendency to list simply species has done 
nothing towards distinguishing faunas. As a result faunas which are 
really distinct and which should be kept entirely separate are merged. 
Critical examination of the biologic features as given in the literature 
of the subject indicate quite clearly that the faunas as usually recognized 
are composite faunas. Inquiry in the fleld shows that such faunas are 
in reality made up of distinct elements. These are not continuous 
through any considerable range, but alternate, much the same way as do 
the general lithologic characters. 
Similar conditions of alternations of faunas have also led to very er- 
roneous conclusions regarding the age of the different parts of the Cre- 
taceous section in the southern Rocky Mountain region, to which atten- 
tion has been recently called. 
