576 DOMAIN VI. CARBONACEOUS. 



mineral substances is often influenced by their 

 gangarts. Mr. Kirwan has observed, and lie 

 has illustrated the observation by many ex- 

 amples, that the soils containing coal are chiefly 

 clay and sandstone, often both together; which 

 are followed*by the rarer instances of coal found 

 tinder trap or basaltin, which may also assume 

 the form of amygdalite; or, by the coarseness of 

 the particles, become a basalton or grunstein. 

 Thick beds of coal have also been found amid 

 the strata of limestone. As the theme is of great 

 importance to national and individual wealth 

 and prosperity, it may be proper to subjoin the 

 brief general view by Brongniart. 



" The coal regions follow in general the same 

 order of composition. L Psammites (micaceous 

 and ferruginous sandstone, with a cement gene- 

 rally of argil,) often large grained: they are not 

 only composed of quartz and mica, but of frag- 

 ments of all kinds of rocks, particularly of fel- 

 spar. 2. Argillaceous and micaceous schisti > 

 presenting on their plates impressions of fishes 

 and vegetables, which generally belong to the 

 families of ferns and grasses. 3. Beds of marl, 

 carbonated lime, or indurated clay. 4. A kind 

 of secondary argillaceous porphyry, which con- 

 tains branches, roots, and even entire petrified 

 trees. 5. Argillaceous iron ore. 6. Rolled 



