102 A. S. Wiliams—Fauna of the Chemung Group. 
The species are as distinct from the ordinary Chemung 
species of New York as they are from those of the Hamilton 
roup below. Moreover, the High-point fauna contains repre- 
sentatives of nearly every species of mollusca known to be 
common to the several different exposures of the Kinderhook 
group in the west. 
The corals are not so well represented in the east. A few 
wise than by considering them geographical extensions of a 
single fauna. 
The facts of the greater predominance of the Kinderhook 
fauna in the west and of the Chemung fauna in the east, of the 
blending of the two in the same strata at Ithaca, of the appear- 
ance, at High-point, of the western fauna, nearly distinct, but 
in a stratum in the midst of typical Portage and Chemung 
rocks, and of the total absence of the western fauna from most 
of the Chemung rocks of New York, all tend to the con- 
clusion that the Kinderhock group records a fauna whose geo- 
graphical center was in the mid-continental area, while the 
typical fauna of the Chemung group had its geographical center 
as far east as the Appalachian region. In at least a part of the 
time when these faunas lived they encroached upon each other. 
The rocks at the base of the Chemung group in central New 
York contain also traces of a recurrent Hamilton fauna, as was 
shown by the autbor in 1881 (see Proc. A. A. A. S., vol. xxx). 
And the species found in this recurrent fauna are mostly among 
those having a wide geographical range in the Hamilton period. 
There are also a few forms which began in the lower or 
middle Devonian, and continued to appear among the species 
of the Chemung group in New York, in some cases the identi- 
cal species, in others by varieties of the type. 
In the latter case we observe that those modifications which 
mark the western types of the Hamilton group, as distinguished 
from the New York Hamilton, are the very peculiarities to 
distinguish the higher Chemung representatives in New York. 
e coarse variety of Atrypa reticularis, called A. aspera var. 
occidentalis Hall, is a case in point. This and the form called 
A, spinosa are the common forms of the upper Chemung. 
Cyrtina Hamiltonensis appears in the western and northwestern 
Hamilton as a large, coarse form, and with the same modifica- 
tion in the Chemung. Of the Orthids, the wider and more 
gibbous Orthis impressa, called O. Jowensis in the west, is typical 
of the Chemung group, and is the western variety. 
