236 



HECEEATIVE SCIENCE. 



Similar "banks of corals, stells, and encri- 

 nltes stxetclied far away from Europe into 

 India, and were widely extended in North 

 and South. America, as well as in the Arctic 

 regions ; and throughout all this wide range 

 the coal-plants grew, and alternated with the 

 sea, and marsh-formed beds. 



Although we have given, in this brief 

 sketch, an outline of the origin of coal, we 

 may still ask what is coal? When the 

 jD;rowth of centuries had formed forest masses. 



exerted, and the quantity of foreign matter 

 present, the bituminous particles partook 

 more or less of a regular symmetrical semi- 

 cylindrical form, like so many squeezed and 

 out-drawn pasty pellets. In the course of 

 time, when the carbonaceous matter took on 

 a stony consistency, these compressed atoms, 

 thus arranged side by side, gave that law of 

 breakage of the coal-mass which is exhibited 

 in the four planes of easy fracture presented 

 to us in every block, and which we so com- 



Lign. 2.- 



-Coal-plants ia " Stony Bind," from the Ashby Coal-fiekl. 1. Volckmannta dislicTia; 2. (Middle 

 specimen) Ncuropleris gigantea ; 3. Asterophylliles longifolia. 



and the decayed trees, closely heaped in the 

 great shallow bays, were floored in by the 

 mud-floods of the rivers, or the silt of the sea, 

 the heat of decomposition and the pressure 

 of the sediment piled above, produced che- 

 mical changes which resulted in the bitumi- 

 nous matter of the rotting wood being sepa- 

 rated or distilled as pure bitumen in innu- 

 merable minute globules, interspersed with 

 vegetable fibre, and sometimes with mud. 

 According to the intensity of the pressure 



monly notice in the easy cleaving of well- 

 warmed coals when we break up or stir a 

 fire. In the fracture of coals, two planes of 

 easiest cleavage are in a longitudinal direction 

 parallel to the bedding of the coal, and two 

 others are at right angles to these, and con- 

 sequently across the smallest diameter of the 

 particles. 



When the coal is very muddy, or much 

 vegetable fibre retained, the particles of crys- 

 tallized bitumen preserve their spherical 



