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ERIE DIVISION. 
IV. ERIE DIVISION. 
§ 1. General considerations in regard to the erie division of the new-york 
SYSTEM. 
A fact of the highest importance, which has been ascertained in regard to the succeeding 
rocks, is that all the heavy beds of limestone are confined to the three inferior divisions 
that have been already described. Calcareous matter is disseminated through some of the 
lower members of the Erie division, and even strata of tolerably pure limestone occasionally 
occur ; still we consider it at least questionable whether any of these thin deposits should 
be treated as distinct limestone rocks. Should they be found to expand and thicken in the 
extension of the shales in which they here occur, in any direction so as to become in other 
places important masses, it would in that case be proper to treat them as rocks. Thus the 
Oriskany sandstone in New-York is quite thin and unimportant, yet in Pennsylvania it 
becomes an important rock. So the Tully limestone, when a more extended series of 
observations shall prove it an important mass elsewhere, will undoubtedly be regarded as 
a distinct rock. At present, however, it is only worthy of notice as a landmark, or as a 
deposit that serves to mark the termination of a group of shales ; as such it is important, 
and it is in some places important in furnishing lime. As a rock, or a member of a system, 
it only requires a passing notice, notwithstanding its fossils may be somewhat peculiar or 
limited to this mass. 
The same remarks will be found applicable to another bed of limestone, that is some¬ 
times associated with the Marcellus shales, the inferior rock of the Erie division. 
The lithological characters of the rocks belonging to this division scarcely differ from 
those of the Hudson-river series. They are shales, brown, black, gray and green : the 
darker colored ones are mostly confined to the inferior part of the division ; the gray and 
green, to the middle and superior portions; while the brown shale forms the superior part 
of the division. The gray beds often contain fine and beautiful flags, suitable for walks, 
window sills, coverings for cisterns and wells, and for a great variety of common purposes 
unnecessary to be particularly stated in this place. 
The Erie division terminates above in a series of green and red sandstones and shales, 
which are known in New-York as the Fifth or Catskill division. The passage is gradual 
and indistinct, and hence it is not well ascertained where the division line should pass, 
or even whether the whole mass constituting' the Fifth division might not with propriety 
be embraced in some general division of the upper members of the New-York system. 
This plan, however, though it is always desirable to limit the number of systems as well 
as rocks, will not probably be regarded as admissible beyond the bounds of this State, as 
the lines of demarkation are more clearly drawn in other parts of the United States and in 
Europe. 
