152 COAL AND COAL-FORMATIONS. 



the vegetable mass has undergone extreme chemical change, 

 or has, as a coal, "been subjected to the heat of igneous rocks, 

 it will less or more be deprived of its gaseous elements and 

 converted into an anthracite. And thus, and thus only, can 

 the great variety of coals occurring in the paleozoic coal- 

 fields of Europe and North America be satisfactorily ac- 

 counted for. 



Beyond the Carboniferous system coals become rare and 

 comparatively unimportant. It is true that in some dis- 

 tricts we cannot fix any very sharp line of demarcation 

 between the Coal-formation and the Old Red Sandstone, but 

 generally speaking the two systems are sufficiently distinct, 

 and it is curious that up to the present time no coal-seams 

 of any thickness have been detected in the latter. Indeed, 

 with the exception of some insignificant bands described 

 by Principal Dawson as occurring at Gaspe in Canada, the 

 Old Red Sandstone is altogether barren of coal, though 

 vegetable fragments are scattered^in some abundance through- 

 out its shales and flagstones. In the Silurian and more 

 highly metamorphosed Cambrian and Laurentian strata we 

 have thin bands and irregular patches of anthracite and 

 graphite ; but though these are generally ranked with the 

 coal family, their vegetable structure has been so obliterated 

 that we cannot say whether they have been formed from 

 terrestrial or marine vegetation, or indeed whether graphite 

 is always certainly of organic origin. 



Here, then, we perceive that Coals, or minerals of the 

 Coal Family, occur in all formations, from the accumulations 

 now going forward on the earth's surface down through 

 every stratified system, whether belonging to tertiary, second- 

 ary, or primary epochs. From peat we pass to lignite, from 

 lignite to true coal, from coal to anthracite, and from anthra- 



