Origin of Cayhunaceuus SJtales. o57 



XXI, — The Origin of the Carbonaceous Matter in Bitumi)ious 



Shales. 



BY JOHN S. NEWISEERY. 

 Re:id April 2d, 1883. 



Among the sedimeiitaiy rocks, there are none in regard to 

 the origin and mode of formation of which there has been 

 more difference of opinion than the bituminons shales. These 

 are typified by theUtica shale of the Lower Silurian, by the Ham- 

 ilton shales of the Upper Devonian, — including the Marcelins, 

 the Hamilton, the Genesee and Gardeau shales of the New 

 York geologists, and their general equivalent, the Huron shale 

 of Ohio, — by the Cleveland shale of the Lower Carboniferous, and 

 by the bituminous shales, with their varieties, blackband iron ore 

 and cannel coal, of the Coal Measures. 



We also find in Colorado a great mass of bituminous shale 

 occupying the central portion of the Cretaceous series, a part of 

 the "Colorado Group." 



These bituminous shales usually contain from ten to twenty 

 ])er cent, of carbonaceous matter, the remainder being clay and 

 very fine sand, with occasional specks of mica. As a general 

 rule, such shales are not very fossiliferous, but the scales of 

 small ganoid fishes and the singular denticles called Conodonts 

 are almost always present, and not unfrequently we find minute 

 flattened, originally spheroidal bodies, which are apparently the 

 spores of plants. In the Utica shale, graptolites are exceedingly 

 abundant, sometimes quite filling the rock ; and trilobites, 

 sponges and Crustacea are sparingly found. 



In the Devonian shales, the most common fossils are Lingulas, 

 Discinas, a small Orthoceras, and bivalves of the genera Avicula 

 and Lunulicardium; sometimes, also, a Pteropod {Tentaculites 

 fissurella) in countless numbers ; all these are minute. In the 

 Huron shale, and recently, also, in the Devonian shales of 

 New York, have been found the remains of large placoderm 

 fishes in considerable numbers ; but vast masses of this- rock 



