36 COAL. 



Coal is classed by geologists among the secon- 

 dary rocks or substances, and is found in region? 

 of secondary formation arranged in horizontal 

 strata. The whole western country is of this 

 character. 



Again. — Its accompaniments, shale and sand 

 -tone 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. 



H\ T drogen gas, or burning springs, are also 



;ound in this region, issuing from strata of schist, 



md are of the same nature, in several respects, 



with the gas obtained from the distillation of coal. 



ir 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 id a degree always 



citified with coal. For the inflammable gas of 



marshes consists of hydrogen and charcoal. 



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



?uing from the earth in its usual state, I set down 

 origin in some measure to coal . 



