AND ITS SUBORDINATE BEDS. 
67 
I deem it unnecessary to describe these beds more minutely, except to remark generally 
that their thickness varies from a few feet to sixty ; the coarse and finer sandstones are about 
sixty feet in their greatest development, and the siliceous sandstone about thirty. The 
beds of roofing slate may or may not be over sixty feet thick. The blue sparry and brec- 
ciated limestone is about twenty or twenty-five feet thick. 
All the above masses are strictly beds, lying parallel to the beds of slate whose strike is 
N. 10° E. by compass. The presence of these beds, their relations to each other, and the 
great mass which embraces them, are facts of sufficient importance and character to lead to 
the separation of this slate from the shales of the Hudson river. To be satisfied of this, let 
the inquirer traverse the rock from west to east: he will usually find, first, a fine greenish 
slate, passing into a coarse siliceous slate, with one or two beds of the coarse sandstone 
with angular fragments; passing on farther, he will meet with a bed of flinty slate, asso¬ 
ciated perhajjs with a few sparry layers of limestone ; then a bed of more perfect sandstone ; 
then, one of liver-colored slates; and still farther to the east, and near the great mass of 
the sparry limestone, he will find the roofing slate. In following this direction, however, 
he will, in the space of fifteen or twenty miles, pass several times over the same beds, 
which are brought up by many successive uplifts. 
The roofing slate had been heretofore classed among the Hudson river rocks or the 
Loraine shales, but later observations have proved in the most satisfactory manner that it 
is a part of the Taconic slate. I was led into this error myself by the discovery of fossils, 
which had much the appearance of the graptolites of the Utica slate, but which I am 
now satisfied are marine vegetables. Those geologists who are well acquainted with the 
different beds of the Hudson river series, will at once see that they do not, as a whole, 
agree with or correspond to those of the Taconic slate ; and though Prof. Rogers remarks 
in his address, that my sections in general correspond with his own, requiring merely the 
restoration of the great curves in order to make the correspondence perfect, except in 
the want of conformity of some of the beds; it may be replied, that although the Hudson 
river shales and Taconic slates may be connected by supplying curves, it is only an acci¬ 
dental coincidence, the fact being perfectly clear that no real similarity can exist in two 
systems, one of which is anterior to the other. And I may very properly remark, that it 
furnishes a lesson well worthy of remembrance even to so learned and accomplished a 
geologist as my friend Prof. Rogers, not to place too much reliance upon the imagination ; 
for certainly it is plain that an inferior system can not be connected with a superior, 
although a certain similarity may exist in regard to order; and though two sections, one 
of which is from the former and the other from the latter, may have coincident masses, still 
from this alone without other kinds of proof, they ought not to be considered identical. 
9* 
