38 
IOWA ACADEMY OP SCIENCES. 
and the abruptness with which an entirely new fauna begins at 
that level. 
(2) Character and Relations of the Lower Fauna .^ — The compo- 
nents of this fauna comprise those forms which, as already 
noted, occur in the Louisiana limestone and the Hannibal shales. 
For the present only the species from the former need occupy 
attention. 
As a whole the fauna is clearly closely related to that occur- 
ring in the Western Hamilton. Some of the species, though 
bearing different names, are in reality identical with typical 
forms from that formation. Heretofore the fossils have been 
found, with few exceptions, perhaps, only in the basal portion 
of what is called the Louisiana limestone, in number 6, a thin 
sandy layer which is lithologically similar to the partings in 
the limestone itself. The results of the latest investigatons 
show that many of the forms extend upward, some of them 
passing practically unchanged through the whole Louisiana to 
the top of the Hannibal. Not a single species of this fauna 
appears to occur in the overlying layer which has been 
regarded as the equivalent of the Chouteau. Many of the forms 
also range downward into the dark colored shale below, which 
is regarded as of Devonian age and which is here separated 
into two parts. A short distance away the shale becomes much 
thicker. 
The general impression derived from the table is that the 
zones 5 to 8 inclusive are faunally very closely related, and 
that the higher ones, 9 to 11, also have close affinities with the 
lower zones. It may be noted in this connection that no 
special effort has been made to determine the full faunas of the 
higher beds, as the critical evidence that was needed was in 
regard to the fauna of the Louisiana (Lithographic) limestone. 
The shales have, however, proved to be remarkably barren in 
organic remains. Towards the top where they become sandy 
a number of the lower species are found. That the shales do 
not appear to be fossiliferous is not remarkable. Since they 
manifestly do not contain abundant remains in a good state of 
preservation they have not been searched so carefully by fossil 
collectors as have the other beds. At Burlington, Iowa, where 
there are excellent exposures and numerous active local col- 
lectors, besides a host of transient ones, the same shales 
remained for half a century without a fauna to be ascribed to 
them. But of late they have been shown to be abundantly 
