PORTAGE GROUP. 
229 
The description of these three divisions will furnish a correct idea of the lithological cha¬ 
racter of the group. At the eastern end of the district the whole series consists of shales and 
shaly sandstones, with some thick-bedded sandstones, corresponding more nearly with those 
above them than the same do farther west. Still it must be acknowledged that in lithological 
characters there is no abrupt change, or evidence of very different conditions in the ocean from 
which they were deposited, from the termination of the Tully limestone, to the final deposition 
of the Chemung group. Shales and sandstones, differing in some degree, it is true, compose 
the whole assemblage. In the lower part these are more intermingled, and the sand is finer; 
while in the higher part of this series, the sand is often coarser, and generally less intermixed 
with shale. The Portage group forms the lower member of this great division, the sandstones 
and shales being less separated than above ; the arenaceous strata are finer grained, and 
always more argillaceous than in the Chemung group. 
When we apply the test of organic remains, we find an equally, or even more strongly 
marked difference in the two groups, and upon this alone a distinction between the two should 
be made. Throughout the whole thickness of the Portage group, which is not less than 1000 
feet, there are but two forms which can be referred to the Brachiopoda; one of these is a 
Delthyris, and the other apparently an Orthis, and both are quite unlike any others which 
have been seen in the rocks above or below. In both the Hamilton and Chemung groups, 
shells of this family are the predominating forms, and they are at least ten times more nume¬ 
rous than any others. In the Portage group the principal forms are Goniatites (fragments of 
several species being known), Bellerophon, and bivalve shells allied to Pterinea? with a small 
Avicula everywhere characteristic, and known in no other rock. 
Considering these facts, it seems desirable to separate these lower rocks, that we may have 
an opportunity of investigating them separately, and of comparing their fossils before we unite 
them with the higher group, which has a very great development, and in which I have never 
seen one of the fossils of the Portage group. 
The higher mass of sandstone of the Portage group, before mentioned, is very persistent, 
being known in Ohio as the Waverly sandstone ; and there, as well as in New-York, it forms 
a line of demarcation between the almost non-fossiliferous shales and sandstones below, and 
the highly fossiliferous sandstones and shales above, which latter are a continuation of the 
Chemung group. From the circumstance that but few of the strata in the Portage group 
contain fossils, they have usually been overlooked, and the rocks on a hasty examination would 
be pronounced non-fossiliferous. 
Along the shore of Lake Erie, the rocks of this group hold a conspicuous place, having 
traced them continuously from near Eighteen-mile creek in Erie county, to Erie in Pennsyl¬ 
vania ; and beyond this they appear at numerous points, apparently being continuous as far 
as Cleaveland in Ohio. Fossils, with the exception of fucoids, are rare throughout this whole 
distance, and it is mainly from lithological characters that the strata are recognized. In Ohio, 
and to the southwest, there is a much greater similarity in the lithological characters of the 
Portage and Chemung groups than in New-York, and there they are not separated by those 
who have described them. 
