THE CARBONIFEROUS. 67 



coal roofs equally testify to the accumulation of coal by the growth of 

 successive forests, more especially o^ Siglllarice. There is, on the other 

 hand, no necessary connection of sporangite beds with Stigmarian 

 soils. Such beds arc more likely to be accumulated in w^ater, and 

 consequently to constitute bituminous shales and cannels. 



" (G.) Lepidodendrun and its allies, to which the spore-cases in 

 question appear to belong, are evidently much less important to coal 

 accumulation than Siffillaria, which cannot be affirmed to have pro- 

 duced spore-cases similar to those in question, even though the obser- 

 vation of Goldenberg as to their fruit can be relied on ; the accuracy 

 of Avhich, however, I am inclined to doubt. 



" On the whole, then, while giving due credit to Prof. Huxley and 

 those who have preceded him in this matter, for directing attention to 

 tliis curious and no doubt important constituent of mineral fuel, and 

 admitting that I may possibly have given too little attention to it, I 

 must maintain that Sporangite beds are exceptional among coals, and 

 that cortical and woody matters ai'C the most abundant ingredients in 

 all the ordinary kinds ; and to this I cannot think that the coals of 

 England constitute an exception. 



"It is to be observed, in cunclusion, that the spore-cases of plants, 

 in their indestructibility and richly carbonaceous character, only par- 

 take of qualities common to most suberous and epidermal matters, as 

 I have explained in the publications already referred to. Such 

 epidermal and cortical substances are extremely rich in carbon and 

 hydrogen, in this resembling bituminous coal. They are also very 

 little liable to decay, and they resist more than other vegetable 

 matters aqueous infiltration, — properties which have caused tliem to 

 remain unchanged, and to resist the penetration of mineral substances 

 more than other vegetable tissues. These qualities are Avell seen in 

 the bark of our American white birch. It is no wonder that materials 

 of this kind should constitute considerable portions of such vegetable 

 accumulations as the beds of coal, and that when present in largo 

 proportion they should afford richly bituminous beds. All this agrees 

 with the fact, apparent on examination of the common coal, that the 

 greater number of its i)urest layers consist of the flattened bark of 

 lS/[//Uari(e and similar trees, just as any single flattened trunk em- 

 bedded in shale becomes a layer of pure coal. It also agrees with the 

 fact that other layers of coal, and also the cannels and earthy bitumens 

 appear, under the microscope, to consist of finely comminuted i)articles, 

 principally of epidermal tissues, not only from the fruits and spore- 

 cases of plants, but also from their leaves and stems. These con- 

 siderations impress us, just as much as the abundance of spore-cases, 



