PALAEONTOLOGY OF NEW-YORK. 
9 
ding; and these being often close and well defined, while the lines of 
bedding are obscure, give it the appearance of nearly vertical stratifica¬ 
tion. This character prevails even when distant from any metamorphic 
influences. These features distinguish the rock from any other in the 
series; and even in its smaller outcrops, the vertical lamination has 
been found a valuable guide in its identification. 
In the upper part we find a gradual increase of calcareous matter, with 
a diminution of the argillaceous material; and it passes, by almost im¬ 
perceptible gradations, to the Schoharie grit, which is marked by the 
presence of numerous fossils. The upper beds of the Cauda-galli grit, and 
also the lower beds of the Schoharie grit, preserve those peculiar mark¬ 
ings which have been termed Fucoides cauda-galli. 
From the base of the Schoharie grit, we begin our investigation among 
the fossils. In this rock we find, for the first time, a small number of 
species which pass upward through the limestones of the Upper Helder- 
berg group, and are more abundant in the Hamilton group( : ). At the 
same time, also, we find a few species which are apparently identical 
with some which we have known in the preceding rocks. These, however, 
are so few, and being comparatively rare, the large number of n,ew spe¬ 
cies of the same genera makes them inconspicuous, and we have essen¬ 
tially a new fauna. 
One of the most marked features of the change of fauna at this period 
is the introduction, or appearance for the first time, of numerous species 
of the Genera Cyrtoceras, Gyroceras, etc., with strongly lamellose or 
fluted surfaces, and which are often ornamented by nodes or spines. 
Some of the Orthoceratites are marked by sharp lamellose rings, and 
some of the Gasteropoda are spiniferous. The Trilobites of the Genera 
(1) Among those which begin their existence in this rock, occurring likewise in the Upper 
Helderberg limestones and passing into the Hamilton group, Orthis vanuxemi ?, Streptorhyn- 
chus chemungensis , Strophomena demissa, S. perplana — S. crenistria, Spirifera Jimbriata*, 
Atrypa impressa =• a variety of the A. reticularis ? while a larger number of species are 
common to the grit and to the limestones above. 
* Two individuals of this Species have been found in the Oriskany sandstone. 
