Abstraction of Nitrogen from the Atmosphere. 87 
posterior to these periods, are found in any country, in sufli- 
cient abundance to merit exploration. 
That coal is a product of vegetation, or organized life, is 
conceded by almost every geologist. know of no good 
argument to show the contrary ; and the arguments in favor 
of its vegetable origin are many. From the abundance’of 
coal, and its being limited to a geological period, we must 
infer a greater degree of heat, and moisture, than existed 
subsequently. 
All the beds of coal are accompanied by impressions ot 
plants. Be the place where found, where it may, these 
plants are not very dissimilar from each other ; and th 
analogous to tropical plants.* This fact shows that the 
degree of heat and moisture was greater, or the plants would 
not resemble those of the tropics. 
There are three kinds of coal in nature ; two of which 
only are used in commerce, with a few local exceptions. 
These coals, are lignite or fossil wood, which is the most re- 
cent kind. he next in age is the bituminous. The oldest, 
and last, is the anthracite. The composition of these coals 
is as follows: Lignite consists of proximate principles ; car- 
bon, bitumen, acetic acid, and water. Its ultimate inciples 
are, carbon and water. Bituminous coal €onsists of bitumen, 
carbon, and water. Its ultimate principles, are carbon and 
water. Anthracite has for proximate and ultimate principles, 
carbon and water. Lignite and bituminous coal are resol- 
vable into anthracite by the application of heat under pres- 
sure. In the lignite, the acid is first decomposed, and finally 
the bitumen ; leaving carbon and water as the products. 
he explanation of these various kinds of coal, as they 
exist in the earth, requi | ter degree of heat 
should have existed, when the oldest of these coals was form- 
ed, than was requisite for the most modern, or the one inter- 
mediate in age and in composition. 
Coal seems to have been deposited in two different modes ; 
first, in estuaries, or hollows, which appear to have received 
the vegetable or coaly matter of the surrounding country.— 
not well acquainted with modern geological observations, may be 
disposed to regard the plants as vegetable matter, which constitutes and oe- 
curs in coal depositions, as the production of tropical regions, transported to 
the places where found. To sach [ refer the memoir of Mr. A. Brongniart, 
* Sur des vegetaux fossilles traversant les couches du terrain houiller,” an- 
nales des mines, troisi livraison, annee, 1. In this memoir, a mass of 
facts is presented, which precludes every opinion of the kind. 
