120 GEOLOGY OF OHIO. 



circumstances — and which is a kind of distillation — are, peat, lignite, 

 bituminous and anthracite coal, graphite and asphaltum, which are 

 solids; carbonic acid, carburetted hydrogen, etc., which are gases. Of 

 these, all the solids, excepting asphaltum, are residual products, while 

 that substance and the liquids and gases are the evolved products, or dis- 

 tillates. Neither of these substances has any definite formula of compo- 

 sition, as each individual specimen may represent a distinct stage of 

 the process of bituminization. The first mineralized solid formed from 

 vegetable tissue is usually called lignite, if derived from wood ; peat, if 

 from herbaceous vegetation. These terms are, however, somewhat vaguely 

 employed ; for while the term peat is used only for the brown, spongy 

 mass — mostly derived from mosses — which is found in our surface bogs 

 and is now forming, the name lignite is given not only to bituminized 

 woody tissue, but to the Tertiary and Cretaceous coals, even though they 

 may have been formed of the same materials and in the samo way as 

 our recent peat beds. 



Such being the relations of the carbon series, it is manifest that to 

 express each one by a distinct formula, as though they were mineral spe- 

 cies or definite chemical compounds, is a miss atement of the truth of 

 nature, and is calculated to create misappreheii-ion. This will be obvi- 

 ous to any one who will compare the hundreds oi careful analyses which 

 have been published of the different hydrocarbons. The nature of the 

 changes which take place in the formation of peat and lignite from veg- 

 etable tissue will be seen by the comparison of typical examples of each 

 given below : 



Vegetable tissue. Loss. Peat. 



Carbon 49.1 21.50 27.6 



Hydrogen 6.3 3 50 2.8 



Oxygen 44.6 29.10 15.5 



Wood. Loss. Lignite. 



Carbon 49.1 18.65 30.45 



Hydrogen 6.3 3.25 3.05 



Oxygen 44.6 24.40 20.30 



In this process the evolved products represented by the loss are water, 

 carbonic acid, and carburetted hydrogen, or petroleum. 



Where peat or lignite have been long buried in the earth they have 

 suffered still further loss and change, and are converted into what is 

 termed bituminous coal, as will be seen in the following example : 



Lignite. Loss. Bituminous Coal. 



Carbon 30.45 12.35 18.10 



Hydrogen 3.05 1.85 1.20 



Oxygen 20.30 18.13 2.07 



