180 ERIE DIVISION. 



IV. ERIE DIVISION. 



^ 1. GENERAL CONSIDKRATIONS IN REGARD TO THE ERIE DIVISION OF THE NEW-YORK 



SYSTEM. 



A fad of the highest importance, which has been ascertained in regard to the succeeding 

 rocks, is thai all the heavy beds of limestone arc confined to the three inferior divisions 

 that have been already described. Calcareous matter is disseminated through some of the 

 lew ei members of the Erie di\ ision, and even strata of tolerably pure limestone occasionally 

 occur : still we consider it at least questionable whether any of these thin deposits should 

 be Healed 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 

 Oriskanv 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. \t 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 lie 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 w r ell 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 "jenoral 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 

 -. will not probably be regarded as admissible beyond the bounds of tins Slate, as 

 the lines of demarkalion are more clearly drawn in other parts of the United Stales and in 

 Europe. 



