GEOLOGY. 207 



it. It is about 50 feet thick in Canada. Those two rock formations, 

 then, which in Canada are not over 1,00 feet in thickness, are the res- 

 ervoirs, holding roek oil, however and whenever formed, in that country. 



Ascending in the geological scale, and passing over into New York, 

 the next stratum of rock yielding bitumen, oil and gas, is there known 

 as the Hamilton Group, about 1,000 feet thick. The oil springs of 

 Western New York, along the banks of its numerous lakes, are mainly 

 in this group of roeks. They have as yet yielded oil only in small 

 quantities for medicinal purposes. But they afford ample scope and 

 verge for exploration. 



Above this group succeed black shales, known as the Genesce 

 Slate, 300 feet thick. The wells of Mecca, Ohio, and others of that 

 region are most probably in this rock. Above the Genesee Slate 

 comes in the Portage Group of slates and sandstones, 1,700 feet 

 thick. The deeper wells of Oil Creek, Pa. will reach the sandstones 

 of this group. 



Still above lie the rocks of the Chemung Group, which are mainly 

 composed of thin-bedded slates and limestones. In its maximum it 

 is 3,200 feet thick, but in Western New York and Pennsylvania it is 

 much thinner, being only about 1,000 feet thick. Much of the oil of 

 Oil Creek is from this group ; 400 and 500 feet of it are seen in the 

 cliffs and hills of Oil Creek, the Alleghany River, and its tributaries 

 above, and in Venango County. 



Measuring the maximum development of all the rocks enume- 

 rated we find between the oil of Canada and Venango County, Pa. 

 6,000 to 7,000 feet of sedimentary rock, all of which bear the ap- 

 pearance of having been deposited in sea water. The entire group of 

 rocks enumerated arc known as the Devonian Series in England. 

 The oil springs of Eastern Canada and New Brunswick, along the 

 Gulf of Newfoundland, are in the upper members of this series. 



Leaving for the present those portions of the United States where oil 

 has been most successfully found, and before coming into the geological 

 strata of the thick and heavy oils, we have on the eastern flanks of the 

 Appalachian Mountains, in Pennsylvania and Virginia, 5,000 feet of the 

 Catskill group of rocks. (Ponent of Prof. Kogers.) Lapping around the 

 southern outcrop of the coal measures of Tennessee, Kentucky, and Illinois, 

 there are 200 feet of the lower carboniferous and 3,000 feet of the middle 

 carboniferous. (Umbral of Rogers.) A total in the aggregate, as meas- 

 ured in Nova Scotia and the United States, of 1,500 feet. Throughout 

 the whole of the series oil and gas springs are found. 



We now come into the true coal measures. These are divided into 

 lower, middle, barren measures and upper, a total of the bituminous 

 portion of 2,500 feet. The lowest member of the coal series caps the 

 highest hills, near the mouth of Oil Creek, and lies about 600 feet above 

 the bed of the creek, or 1,300 feet above the third sand rock, which is 

 the most abundant oil-producing stratum. At the Kiskiminetas, Slippery 

 Rock, Butler Co., Pa., Beaver & Smith's Ferry, oil is in the lower coal 

 measures 800 feet thick. High up the Kiskiminetas and on the Mo- 

 nongahela River, oil is found in the middle coal series 1,000 feet thick. 

 At Marietta, Ohio, and in the oil region around the strata of the upper 

 coal are the productive series. 



To conclude, then, oil is found through 24,000 feet of rocks, as mcas- 



