V ON THE FORMATION OF COAL 139 



Now let us suppose two such slices to be 

 prepared from our lump of coal — one parallel 

 with the bedding, the other perpendicular to it ; 

 and let us call the one the horizontal, and the 

 other the vertical, section. The horizontal section 

 will present more or less rounded yellow patches 

 and streaks, scattered irregularly tlirough the 

 dark brown, or blackish, ground substance ; while 

 the vertical section will exhibit mere elongated 

 bars and granules of the same yellow materials, 

 disposed in lines which correspond, roughly, with 

 the general direction of the bedding of the coal. 



This is the microscopic structure of an ordinary- 

 piece of coal. But if a great series of coals, from 

 different locahties and seams, or even from 

 different parts of the same seam, be examined, 

 this structure will be found to vary in two 

 directions. In the anthracitic, or stone-coals, which 

 burn like coke, the yellow matter diminishes, 

 and the ground substance becomes more pre- 

 dominant, blacker, and more opaque, until it be- 

 comes impossible to grind a section thin enough 

 to be translucent ; while, on the other hand, in 

 such as the " Better-Bed " coal of the neigfhbour- 

 hood of Bradford, which burns with much flame, 

 the coal is of a far lighter colour, and transparent 

 sections are very easily obtained. In the browner 

 parts of this coal, sharp eyes will readily detect 

 multitudes of curious little coin-shaped bodies, 

 of a yellowish brown colour, embedded in the 



