ONONDAGA-SALT GIIOUP. 165 



which require to be broiiirht toj^ethcr before the eliloriiK> of sodium can be obtained. 

 We arc obliged to remain in darluiess on this subject ; while upon the origin of the other 

 saline and acid springs, there is no doubt but that they are formed from the decomposition 

 of the materials in or of the rock itself.* 



General remarks on the middle and upper members of the Ilelderberir division. It has been 

 useful, up to this point of my description of the New-York system, to throw many of its 

 series into groups, which, mineralogically considered, have some striking characters in 

 common. Thus the last series described consists of four, and perhaps more mcuibers, 

 which graduate into each other : they may be quite different apparently at their extremes, 

 still we are unable to discover where it would be necessary to consider them as distinct 

 rocks. When, however, we reach the rocks which form the Helderbcrg and Schoharie 

 ranges, beginning with the Pentamerus limestone, we find it necessary to abandon the 

 plan of throwing the series into groups, and to adopt that of describing the succeeding 

 rocks as distinct individual masses. Limestones, it is true, predominate, and we might 

 describe them under some such appellation as this, namely, the Schoharie limestone group, 

 were it not that the limestones resemble each other so faintly, that the combination of this 

 common name would form an assemblage as heterogeneous as possible. If, for example, 

 we compare the Delthyris slialy limestone with the Onondaga limestone, we may sec at 

 once that they are incongruous rocks. So the same may be said of the Pentamerus and 

 Onondaga limestones ; and finally, no two of the rocks can be grouped together without 

 violating some principle of classification. But what still makes the difficulty greater, is the 

 presence of three beds of anomalous sandstones, which, neither lithologically, nor by their 

 fossils, can be associated together, or with the limestones which are adjacent to them. For 

 these reasons, then, the succeeding rocks of this division are described individually as inde- 

 pendent rocks. It is not intended, however, by these remarks, to convey the idea that 

 there is nothing in common among them ; for some fossils pass upwards through tv/o or 

 more rocks, and thus link them together by conditions which must have been somewhat 

 similar at the period they were deposited. 



Metamorphic rock. At Syracuse, a mass resembling serpentine appears in the gypseous 

 rocks : it is yellowish green, passing into deep green with a tinge of blue. It softens and 

 whitens on exposure to the weather. It eflfervesces briskly with acids, and hence contains 

 considerable carbonate of lime. The interior is hard, and sometimes siliceous and ex- 

 tremely tough. Mica, hornblende, and indeed very well characterized granite, have been 

 observed in a portion of this rock.f It takes a fine polish, and would form a beautiful ser- 

 pentine marble if it was of a vmiform texture and hardness. The origin of this rock is not 

 well determined. Mr. Vanuxem regards it as having been formed by a chemical union 

 of its elements in solution in water. This view is adopted in preference to that of an 



* The green shales, and a part of the Onondaga-salt group, were inadvertently placed in the list of rocks which 

 compose the Ontario division, p. 141. 



t Vanuxem's Report, p. 109. - ' . •, • 



