36 COAL. 



Coal is classed by geologists among the secon- 

 dary rocks or substances, and is found in regions 

 of secondary formation arranged in horizontal 

 strata. The whole western country is of this 

 character. 



Again. — Its accompaniments, shale and sand 

 stone are the principal rocks, besides lime and 

 gypsum. 



Black shale which burns in the* fire, and which 

 derives its color from the bitumen with which it is 

 impregnated, is to be seen in various places. 



Bituminous springs and oil stones exist in this 

 country. 



Hydrogen gas, or burning springs, are also 

 found in this region, issuing from strata of schist, 

 and are of the same nature, in several respects, 

 with the gas obtained from the distillation of coal. 

 Sir Humphrey Davy ascribes the quantity of gas 

 thus spontaneously extricated, to the consolidation 

 of this coal, effected under a great pressure ; and 

 even when this substance owes its origin in some 

 measure to other causes, it is in a degree always 

 identified with coal. For the inflammable gas of 



marshes consists of hydrogen and charcoal. 



Whenever I see this gas in a state of ignition, or 

 issuing from the earth in its usual state^I set down 

 its origin in some measure to coal. 



