NEW-YORK TRANSITION SYSTEM. 99 



CHAPTER V. 



NEW-YORK TRANSITION SYSTEM. 



Sedimentary Rocks of the Northern Counties belong to the loioer part of the Transition 

 System, unciform only one Group. — Lithological characters. — Fossils. — Potsdam Sand- 

 stone the loioest member : Limestones succeed; Shales next, the upper portion Sandstone. 

 — Thickness of the whole mass. 



The Transition rocks of New-York constitute, as a whole, the most perfect system which 

 has hitherto been describee!. 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 which 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 geographical names. To this custom there appears but few objections, so 

 long at least as descriptive or characteristic names ar-e 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 

 gi-oup, 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 



