326 president's address. 



There is another subject, which it has struck me might, espe- 

 cially in this district, be profitably investigated by our members ; 

 that is, the structure of the many varieties of coal, when examined 

 microscopically. It is a subject which, as you are probably 

 aware, has, for some time, engaged the attention of many men of 

 science in Edinburgh ; and the opinions of those scientific men 

 have been almost as various as the speakers, — showing how much 

 yet remains to be achieved in this department. The particular 

 mineral about which the discussion was originally raised, is, I 

 have no doubt, both in its geological relations, its chemical con- 

 stitution, and its economical appliances, coal — one of the numerous 

 varieties of coal ; for they are probably as numerous as are the 

 varieties of sand, lime, or any other stone. It is, I consider, im- 

 possible to define whether a substance is or is not coal, by the 

 proportions of its various constituents, any more than by the 

 structure it displays under the microscope. 



Perhaps the term may be properly confined to those inflam- 

 mable strata, which, there can be little doubt, are of vegetable 

 origin ; not to limit it, as was attempted by some learned men 

 in Edinburgh, to those which show only the woody structure of 

 Coniferce, or to any other vegetable structure in particular ; for the 

 varieties of vegetables which assisted in forming the ancient beds 

 of coal were probably, as indicated by the remains found in the 

 coals and their associated beds, very numerous; more so, consider- 

 ing the tropical vegetation which they indicate, than will, in future 

 ages, be discovered in the beds of coal which, we may presume, 

 will be formed out of our beds of peat. But, even in them, 

 will be found very various structure. In some, the woody will 

 prevail, as many trees — oak, birch, pine, alder, (fee, are imbedded 

 in them ; others, again, are principally composed of heath and 

 fern, mosses and sedges. As Professor Balfour very judiciously 

 remarked, at a meeting of the Koyal Society in Edmburgh, when 

 this question was discussed, " That to give an accurate definition 

 of coal, is simply impossible. Coal includes many kinds of 

 combustible materials, derived from plants ; not from Coniferce 

 alone, but from the Stlgmaricej and many others. So abundant 

 indeed, is the coal Flora, that no less than 500 coal plants have 



