ORIGIN OF THE CHOUTEAU FAUNA 285 
the fossils? Since the faunas are not the same it is necessary 
to assume some kind of barrier to separate them if they were 
contemporaneous. 
But there seem to be very good reasons for continuing to 
believe that the two faunas are not contemporaneous, three of 
which are as follows: 
1. The general facies of the fauna (generic as well as spe- 
cific) is that of the typical Carboniferous faunas of both 
America and Europe, while the Chemung fauna is typically 
Devonian. 
2. Several of the genera and species of the Chouteau fauna 
are not known in any Devonian rocks of America or Europe, 
but are present in other Carboniferous rocks of both America 
and Europe. 
3. The other faunas which present closest relationship to 
that of the Chouteau are the Kinderhook, Marshall and Waverly, 
and wherever these faunas are known to succeed: fossil-bearing 
rocks in continuous sections, they are above the Chemung faunas. 
Until some evidence is at hand to show that one or other of 
these propositions does not represent the facts, it would seem 
to be necessary to regard the Chouteau as of more recent age 
than the Chemung of New York. 
The second point, the dual origin of the Chouteau, seems to 
be a legitimate extension of the general principle assumed by me 
in explaining the cuboides* and succeeding faunas in New York 
state. It was with the expectation of finding this to be the 
fact that I gave the paper the same searching scrutiny which I 
found it necessary to give my own notes on the Cuboides fauna 
before I published them. As Mr. Weller states that he believes 
“the key to the whole problem (of the origin and evolution of 
the Mississippian fauna) is to be found in the dual origin of the 
faunas” as set forth in his paper (p. 915), the importance of 
making sure that there was a dual origin is apparent. 
If, however, we have no evidence of any further duality of 
origin than that supposed to account for the Cuboides fauna in 
*The Cuboides Zone and its Fauna, Bull. Geol. Soc. Amer., Vol. I., pp. 481-500. 
