CATSKILL GROUP. 65 



vania covered with the Chemung. The rocks in nearly all localities emit a bitu- 

 minous odor on percussion, and petroleum often exudes from the crevices. The oil 

 and gas products are the same in the Chemung as in the Portage. The gas and 

 the oil had the same origin. They are both hydrocarbons. They were both de- 

 rived from vegetable and animal organisms. Wherever shales are found con- 

 taining carbonaceous matter, evidence of these products may be obtained. It is 

 possible the gas was first produced, and from it the petroleum has been derived, 

 making the latter a secondary product; but the evidence seems to prove they were 

 both formed at the same period of time, and during the decomposition of the 

 organisms, and before the mud had indurated or hardened into rock. And the 

 evidence also seems to prove they were derived almost wholly from marine plants, 

 for the shales bearing the greater number of fucoids are those to which we ascribe 

 the greater supplies of hydrocarbons. The sandstones which overlie these shales 

 are porous and capable of holding from one-eighth to one-tenth their bulk of pe- 

 troleum, which is sufficient to account for the flowing wells of Pennsylvania which 

 are bored until they penetrate the sandstone. Many of the wells penetrate only 

 the Chemung sandstone, though the oil is derived from the shales of the Portage 

 as well as from the Chemung. The supposed connection of petroleum and gas 

 with anticlinal axes, or synclinal ones, has not been verified by observation, nor 

 supported with reason, neither are they dependent upon faults or crevices, and 

 much less has the depth of the well any connection with the level of the sea. 

 Wells are as valuable when bored below the sea level as they are when the proper 

 rock is struck above that horizon. 



CHAPTER XXIV. 



CATSKILL GROUP. 



§ 136. This Group was named by Emmons from the Catskill Mountains, and 

 quite fully defined by Vanuxem in 1842. It consists of sandstones, shales, slates, 

 conglomerates, and impure limestones. The prevailing color of the arenaceous 

 portion is brick-red, though all of it is more or less colored with iron, and the 

 shales are gray, olive-red, or green. It exists only in a few counties in South- 

 eastern New York, in the Catskill Mountains, where it has a thickness of 3,000 

 feet, and dips rapidly toward Pennsylvania, where it reaches a thickness of 7,500 

 feet, and soon disappears. It does not extend west of the [Genesee Valley in 

 New York, and is wholly unknown on any part of the continent west of that State. 

 It is conformable with the Chemung, and is distinguished only by the change in 

 lithology, and by the fossils. No Corals, Crinoids, Brachiopods, or Trilobites have 

 been described from it, and only a few Lamellibranchs. The land-plants are gen- 

 erally very poorly preserved. The fish remains are relied upon to really prove 

 the rocks belong to the Devonian rather than to the Subcarboniferous age, and 

 though these are rare and poorly preserved, they show it is the equivalent of the 

 Old Red Sandstone of England, and therefore Devonian. In some places the sand 

 is cemented and forms a grindstone grit, and there are hard concretionary masses, 

 and strata unequally hardened, that weather into picturesque rocks. The Group is 



