Geology and Mineralogy. 308 
The passage from the red rocks to the gray sandstone and con- 
glomerate is gradual, with alternations of red and gray rocks, and 
does not afford any strong line of demarcation. 
The remains of Holoptychius, in the form of bony plates, frag- 
ments of bone, etc., extend through a thickness of more than two 
hundred feet. 
In its western extension, the red rock, with its alternations of 
green and mottled beds, shows a gradual thinning, and finally 
seems to be lost entirely. 
One of the greatest difficulties met with in this investigation, 
has been the occurrence of red and greenish shales in the Chemung 
and Portage beds; and the finding of gray beds with Chemung 
fossils at an elevation of at least one hundred and fifty feet above 
the base of the red rocks, which had always been referred to the 
Catskill formation. 
We have finally, however, ascertained, as I believe, the limits of 
the formation, and though not always in strong contrast with the 
rocks below, we have been guided both by physical and biological 
conditions. 
Inthe interval between well-marked Chemung and typical Cats- 
kill, there are beds of intermediate character, and we sometim 
find a few fossils of the lower rocks. e same means of distine- 
tion do not occur in all localities. Tn some places the indications 
h 
cardites Catskillensis, The occurrence of this fossil may, in we 
opinion, be relied on as characterizing the base of the Catskill 
formation, while the Holoptychius marks the beds above, but still 
18 not known above the middle of the formation. 
Another question, involved in this investigation, has been the 
determinations of the relations of these red rocks to the superior 
sandstones and conglomerates, which in eastern New ork and 
ra 
I 0 may or may not be a continuation of the former. i 
n some localities in the border counties of western Pennsylvania, 
i y 
Indeed, trom the little I have seen, I should say, that in the 
ante referred to, there are more species of fossils passing from 
¢ Upper Chemung into the Waverly formation, than there are 
Species passing from the lower to the upper division of the Che- 
) proper, 
fc, Jduestion is of great interest in view of the supposed horizon 
fo Carboniferous forms; but if we are able to substantiate the 
Tegoing proposition, I think it will be shown that the Chemung 
