DESCRIPTIONS OF THE FORMATIONS. 33 



10 c, Genesee, (Black yiate of the west and south). This is a great 

 development of argillaceous fissile black slate. Where its edges only are exposed, 

 it withstands the weather for a great length of time, and often presents mural 

 banks in the ravines, river-courses, and upon the shores of lakes. When the 

 surface of the strata is exposed it rapidly exfoliates in thin even laminae. On 

 disintegration it is often stained with iron, owing to decomposition of pyrites, but 

 in many instances, and the greater number of localities, it retains a deep black 

 color. In this it is distinguished from some beds of black slate in higher 

 situations, which always become stained with hydrate of iron on their edges, 

 and upon the surface of the laminae. In color and general character it greatly 

 resembles the Marcellus shale, and, aside from position, it would be difficult to 

 distinguish the two, in the absence of fossils. It forms no conspicuous feature in 

 the scenery or topography of the general surface. In ravines, and river and lake 

 banks, it is usually seen in connection with the rocks below or above. Its greatest 

 development, and a point where it appears more prominently alone, and the typical 

 locality from which it was named, is at the opening of the gorge of the Genesee, 

 at Mount Morris, where it is seen in the perpendicular cliffs for more than a mile 

 in length. See note No. 112, New York. Another great exposure of the 

 Genesee slate is along the Cayuga Southern Railway south of Ludlowville, where 

 it shows from eighty to one hundred feet thick, with the Tully limestone 

 below and the Portage shales above it. See note 83, New York. The mass 

 decomposes much less rapidly than the soft calcareous Hamilton or Moscow 

 shales below it, and the thin slaty laminae resist atmospheric action a long time. 

 In lithological character it is entirely uniform, having, from Cayuga Lake to Lake 

 Erie, the] same deep black color and laminated slaty structure, nor is there any 

 change in its organic remains. Its fossils in Indiana are precisely identical with 

 those of New York. Hall 218. 



There are few formations in Central New York of which the limits are so well 

 denned as this, lying between the Tully limestone below, and the sandstone flags 

 of the base of the Portage group, above. It may also readily be found by the 

 black color and slaty fracture. This shale has been regarded as the main original 

 source of the petroleum in the oil region of Ohio and Western Pennsylvania, but 

 there is reason to believe that part, at least, of the supply of these regions has 

 come from the Corniferous limestone below it, as maintained by Dr. Hunt. 



All through the western and southwestern states there is always found a 

 BLACK SHALE, which is often the only representative of the Devonian rocks. 

 This is generally considered to be 10 c. Genesee. It is very remarkable that a 

 formation of its composition, of so inconsiderable a thickness, and otherwise so 

 unimportant, should be so widely extended, and retain throughout its character 

 unchanged as a black shale. The researches of Dr. Newbery in Ohio tend to show 

 its fossils to be of theTortage type. It is there 350 feet thick, and he pronounces 

 it to be the equivalent of the Genesee and lower Portage. All the divisions of the 

 Hamilton group, Marcellus, "Hamilton and Genesee, are converted, by exposure, 

 into a deep soil of an excellent quality for agricultural purposes, sometimes quite 

 hilly, but forming smooth land free from stones. Some of the finest wheat-growing 

 and hop-raising land in New York is on the Hamilton, and its rich shales have 

 been carried south by drift and diluvial agencies, and spread over the Genesee, 

 Portage and Chemung, greatly to their improvement. 



