r 

 364 Origin of Carlonaoeous Shales. 



all participation in the process of tlieir formation ; and we must 

 concede not only the possibility but the probability that the 

 streams, lakes, and shallow bays, where the cannel and bitu- 

 minous shales accumulated — in former times as now — were 

 crowded with the microscopic forms of plant-life, which left a 

 residuum with the disintegrated tissue of the larger plants. 



The cannels as a whole differ from cubical coals not only in 

 physical structure, — lacking the lamination and pitchy bril- 

 liancy, as well as containing more ash, — but in chemical compo- 

 sition, since they yield a larger amount of volatile matter — gases 

 and oils — and gases which have higher illuminating power. 

 This, which is true of all cannels, is conspicuously so of the 

 Torbane Hill cannel of England and the "Hartley mineral," 

 " Wollongongite," from Australia. For example, the best cu- 

 bical caking coals, such as are generally employed for the manu- 

 facture of gas, like the Pittsburgh or Westmoreland coals (and 

 which are preferred, as they yield a fair volume of good gas and 

 leave an excellent coke), furnish about 10,000 cubic feet of gas 

 to the ton, while the cannels yield as much as 12,000 cubic feet, 

 and the Wollongongite 15,000. These differences are doubtless 

 in part due to the kind of vegetation from which the carbona- 

 ceous material was derived; the parenchymatous tissue probably 

 furnishing more volatile matter than the ligneous, and the 

 algae perhaps more than the plants higher in the botanical 

 scale. We can imagine, also, that certain plant-tissues which 

 have contributed to the formation of such deposits as the Aus- 

 tralian shale, may have been impregnated with hydro-carbons 

 elaborated by vital processes, such as the resins. These must, 

 however, be extreme and rare cases, and the differences between 

 various coals and carbonaceous shales are probably differences of 

 degree rather than of kind. , 



The spontaneous emission of carburetted hydrogen and petro- 

 leum from bituminous shales is so general that hundreds of lo- 

 calities might be cited where it may be observed ; indeed a 

 belt of oil-wells and gas-springs marks the line of outcrop of 

 each of these beds of bituminous shale of whatever geological age. 

 The organic portion of the shales, like all other organic matter, 

 being in a state of unstable equilibrium, is constantly decom- 

 posing, either by direct and comjjlete oxidation, or by a sort of 



