152 



FOSSIL HYDRO-CARBONS, 



With a few, and those rather questionable, exceptions, the fossil hydro- 

 carbons were originated by the vegetable kingdom ; and I shall, therefore, 

 at once proceed to enumerate the most prominent, and briefly describe their 

 peculiarities. 



Coals. 



Coal is by far the most considerable, as well as the most important, of 

 the fossil hydro-carbons. It is found disseminated in different parts of the 

 earth's crust in layers, or strata, of varying thickness, but chiefly in that 

 geological formation termed, from this very circumstance, the carboniferous 

 system. Scarcely a country on the globe but possesses coal-beds to some 

 extent, yet to England has fallen the lion's share of these useful deposits, 

 as the dark portions of our geological maps abundantly testify. In many 

 instances, the vegetable origin of coal is so evident, that perfect trees are 

 sometimes found imbedded in the mass, completely carbonised ; and so 

 abundant are these plain indications of former vegetable life, that geologists 

 are thereby enabled accurately to describe the different species of plants 

 which flourished in those remote ages. The Coniferous order, or Pines, 

 contributed largely to our supplies of coal : Tree-ferns, Palms, Reeds, and 

 other plants, mostly of gigantic size, also entered freely into the formation 

 of our coal-fields. 



Of coal there is a very great variety, as might be naturally expected from 

 the several peculiarities of the plants producing it ; and, although I have 

 no space sufficient to include any elaborate account of the different sorts of 

 coal, the following table will convey some general idea of the special 

 varieties as well as the chemical constituents of some of the principal coals 

 of Great Britain : 





Carbon. 



Hydrg. 



Oxygen. 



Nitrog. 



Siuphr. 



Ashes. 



Sp. Gr. 



Non-Bituminous, or 

















Anthracites. 

















Valais - - - - 



92-56 



333 



2-53 



— 



— 



1-58 



1-348 



Vizille - - - - 



94-09 



1-85 



— 



2-85 



— 



1-90 



— 





91-44 



3-46 



2-58 



0-21 



0-79 



1-52 



1-375 



Pembrokeshire - 



94-18 



2-99 



0-76 



0-50 



0-59 



0-98 



1-4119 



Semi-Bituminous. 

















Cannel Coal - - 



76-25 



5-50 



13-83 



1-61 



— 



2-81 



— 



„ Wigan - - 



79-83 



6-08 



7-24 



118 



1-43 



4-84 



— 



Bituminous. 

















Llangennech - - 



85-46 



4-20 



2-44 



1-07 



0-29 



6-54 



— 



Ebbw Vale - - 



89-78 



5-15 



0-39 



2-16 



1-02 



1-50 



1-275 



Broomhill - - - 



81-70 



6-17 



4-37 



1-84 



2-85 



3-07 



1-25 



Wallsend - - - 



76-09 



5-22 



5-05 



1-41 



1-53 



10-70 



1-20 



The most valuable coals for general purposes are those which 



