Geological Reports of the State of New York. 229 
A. The Trenton limestone is an important rock for its marble, 
in Schenectady County, and particularly in Saratoga County. It 
is a fine grained and durable stone. On one of the strata of it at 
Glen’s Falls on the Hudson, the upper surface contains marks 
“like those produced in soft mud by drops of rain.”—Report, p- 
97, Mather. ?ipple marks are shown on “ brown sandstone on 
the road from Cattskill to the Mountain House, one mile above 
the toligate.” p. 85. The chloritic and talcose rocks of the west- 
ern part of the valley of the Hudson, are considered by Prof. 
Mather, as “metamorphic with intrusive rocks interstratified :’ 
and he extends the metamorphic rocks into the western part of 
New England. pp. 93 and 96. In this opinion he is opposed by 
‘some of our distinguished geologists, and cannot be followed with- 
out far more and much stronger proof than has yet been offered. 
Indeed it seems obvious that the metamorphic theory is an easy 
method of breaking down the usual distinctions of the rocks. A 
fine section of the rocks “from the summit of the Cattskill Moun- 
tain, south of the Mountain House, to Cattskill Creek,” is given 
on pages 78-81, Mather. 
5. The report of the paleontologist contains very important 
matter, and some interesting corrections. 
Mr. Conrad distinguishes our rocks of the Silurian system, “for 
the sake of convenience,” into three subdivisions, the Lower, 
Middle, and Upper, Silurian series ; it seems also to be quite a 
natural arrangement. The danger is that the classification has 
been made too early, and that adequate examination has not set- 
tled the entire distinctness of all the series. A great proportion 
of them however are satisfactorily ascertained. ‘There is some 
doubt about the termination upwards of the Lower series. It is 
limited by the Pentamerus oblongus limestone in the report, and 
the lowest stratum in the Middle is made Rochester shale. If 
we understand it, this Pentamerus limestone at Rochester is to- 
wards the lower part of the shale, and at Lockport is found en- 
tirely above the Rochester shale, which is much thicker there 
than at Rechester; there would be no diffculty in the natural 
arrangement in making the Red or Medina Sandstone the upper 
stratum in the Lower Silurian.’ But the Pentamerus limestone 
must go with it, in whatever series it is placed. 
» On-p. 31 is a tabular view of the whole series, with the cor- 
responding rocks of Murchison, and the characteristic genera of 
