Ingredients in Banded Bituminous Coal. 483 



of them (with the possible exception of vitrain) actually homogeneous, nor 

 are chemical molecular units, they do not even approximately represent the 

 crystals in a petrological section of a rock ; nevertheless, when represented 

 on a low scale of magnification and in diagrammatic fashion, it may not be 

 devoid of suggestiveness to compare such sections with those so useful to 

 petrologists. 



Text-figs. 1-4. — Diagrams of micro-photographs of sections of " streaky " bituminous 

 coal, indicating the characteristic distribution of the four ingredients : c, clarain ; 

 d, durain ; /, fusain ; v, vilrain. 



I hesitate to elaborate the matter at this early stage, but it seems possible 

 that we have here a first step in the building up of an exact knowledge of 

 the "physiography of coal sections," though the nature of the case debars 

 the development of the theme from following quite the lines of the " micro- 

 scopical physiography of minerals " laid down by Eosenbusch. 



While the present recognition of four distinct ingredients in coal is, so far 

 as I am aware, new, many authors have noted the banded appearance of 



