420 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



appears to be a bed of coal in the process of formation. He con- 

 sidered coal as of mineral origin. 



Dr. Stevens stated that chemists had found it necessary, in the 

 first place, to define what thej mean by coal, because there are 

 so many different substances called by that name. Any substance 

 containing more than fifty per cent, of carbon is called a coal. 

 If it contains more than fifty per cent, of earthy matter it is 

 called a shale. A coal containing a considerable proportion of 

 bituminous substance is called bituminous coal. The carbon that 

 is found in coal I suppose to have been invariably derived from 

 pre-existing vegetables ; and the bitumen to have been derived 

 either from vegetable or from animal matter, or both. No animal 

 deposits are found in anthracite coal, but, examined microscopi- 

 cally, the fibre of the wood can be perceived in the coal itself. 

 Anthracite coal contains bitumen which has been expelled from it. 



If we examine the great anthracite basin extending westward 

 from the Delaware river, we shall find that at the eastern end it 

 is pure anthracite, but that as we proceed westward bitumen is 

 found in it in constantly increasing proportions, until at last it 

 has gradually become a true bituminous coal. There is a coal 

 mine in North Carolina, belonging to a later geological epoch 

 than the coal fields of Pennsylvania. This is one of the most 

 highly bituminous coals in America. This coal field is penerated 

 by dykes of columna trap, and it is found that just so far as the 

 heat of the trap has penetrated the coal has lost its bitumen 

 and become anthracite coal. 



At the time of the formation of the coal beds in the United 

 States the whole territory was sunk down very nearly to a level 

 ■with the Atlantic ocean, and the interior was'occupied by a great 

 basin, a ^prolongation of the Gulf of Mexico. This relation of 

 land and water would give a climate of the character of that of 

 Spain. An immense amount of vegetable matter grew, and 

 especially of those plants which we now call peat, forming plants 

 and mosses. After a sufficient amount of this vegetable matter 

 had been formed to produce a bed of coal, there was a submerg- 

 ence of the American Continent, sufficiently to produce a layer 

 of shale, or slate, or limestone, or sandstone. And it was under- 

 neath the waters of the ocean that the chemical changes took 

 place which converted this peat into coal. Every bed of coal 

 has beneath it a bed of fire-clay, which was the soil in which the 

 plants, from which the coal was produced, grew. Nowhere, in 



