170 NEW YORK STATE MUSEUM 



organic matter in the form of hydrocarbons, and occasionally carry 

 so much of these that they may be of economic value for the produc- 

 tion of oil by artificial distillation. In nature the process by which 

 organic matter is converted into oil and gas goes on very slowly, 

 but once under way it may continue for indefinite periods of time 

 with cumulative results. 



A large mass of shale may thus be considered favorable to the 

 generation of oil and gas, but it is not necessarily significant of their 

 existence in any locality in economic quantity. For this it is also 

 essential that a suitable repository or place of storage be provided. 

 Shales ordinarily are ill adapted for this purpose; they have too 

 little pore space, and under pressure from an overlying load of 

 sediments, their joints and seams, which near the surface afford 

 some room for water, become tight through movements of the mass. 

 Limestones, likewise are usually closely textured, but often contain 

 cavities and openings produced by solution of underground waters, 

 which may be connected into a more or less continuous series by the 

 natural joints and bedding planes. They may have consequently 

 a fairly high storage capacity and show considerable persistence in 

 yield. The best materials for holding gas, oil or water are sand- 

 stones and unconsolidated beds of sand, whose porosity in individual 

 examples ranges from 4 or 5 per cent to about 30 per cent. Their 

 absorbing power varies with the size and the shape of the grains 

 and the conditions with reference to bond. Estimates of the porosity 

 of the oil sands of Pennsylvania seem to converge aroimd 10 per 

 cent as an average. The effective porosity is greater for gas than 

 for oil since the movement of the former through the small openings 

 is not affected by friction to the same extent or by capillarity. 



The potentially important gas horizons are to be found in the 

 great succession of Paleozoic rocks which spread over all the State 

 west of the Hudson river with the exception of the Adirondack 

 Highland on the north, where the rocks like those of the Hudson 

 Highlands are of Precambrian age and of igneous or metamorphic 

 character. 



Neither the Adirondacks nor the Hudson Highlands hold any 

 possibilities for the production of gas or oil. On the borders of the Adi- 

 rondacks and for several miles outward the lower Paleozoic sedi- 

 ments which overlap on the older crystallines do not attain sufficient 

 thickness to store any large supplies of gas. West of the Black 

 river and south of the Mohawk, however, the sedimentary succession 

 rapidly thickens with the appearance of new and higher formations. 



Thus the Precambrian basement in the vicinity of Pulaski, Oswego 



