NEW-YORK TRANSITION SYSTEM. 
99 
CHAPTER V. 
NEW-YORK TRANSITION SYSTEM. 
Sedimentary Rocks of the Northern Counties belong to the lower part of the Transition 
System, and form only one Group. — Lithological characters. — Fossils. — Potsdam Sand¬ 
stone the lowest member: Limestones succeed; Shales next, the upper portion Sandstone. 
— Thickness of the whole mass. 
The Transition rocks of Nevv-York constitute, as a whole, the most perfect system which 
has hitherto been described. To be satisfied of the truth of this assertion, we have only to 
trace out the rocks which successively appear on the southern slope of the Adirondack range. 
Proceeding from the base of this range, at the most northern outcrop of the lowest of the 
sedimentary rocks, in a southwesterly direction towards Pennsylvania line, we pass over an 
unbroken series, which fills up the space geologically between the primary and the old red 
sandstone. In the whole space, such is the order and regularity in the succession, that we meet 
with no unconformable masses, nor sudden and abrupt passages from one group or series of 
rocks to another. There is a gradual sequence or transition from one mass to another ; so 
much so, that it is indeed difficult for the geologist to determine to which series a given rock 
belongs. 
The remarkable series whicli fill up the. space between the Primary and the Old Red Sys¬ 
tem, constitute together the New-York Transition System. It is composed of several groups, 
which, as they cannot be considered strictly natural, it becomes necessary to define their limits 
arbitrarily, and to bring to our aid geographical boundaries ; observing to draw the boundary 
lines, when it is possible, through those, neutral planes where the masses appear to coalesce. 
To these geographical ranges, series, or groups as they are usually termed, it has become 
customary to give geographieal names. To this custom there appears but few objections, so 
long at least as descriptive or characteristic names are so difficult to be obtained, and so likely 
to prove productive of error^ or at least of uncertainty. They answer the present purpose, 
and serve one good end; that of directing the inquirer to those localities where a particular 
group, or individual rock, is best developed, and its relations best disclosed. 
The rocks of the northern counties, or those which form the Second Geological District of 
