v.] ON THE FORMATION OF COAL 95 



mass of the coal is made up of an accumulation of tlie 

 larger and of the smaller sacs. 



But, in one and the same slice, every transition can 

 be observed from this structure to that which has been 

 described as characteristic of ordinary coal. The latter 

 appears to rise out of the former, by the breaking-up 

 and increasing carbonization of the larger and the 

 smaller sacs. And, in the anthracitic coals, this process 

 appears to have gone to such a length, as to destroy the 

 original structure altogether, and to replace if by a com- 

 pletely carbonized substance. 



Thus coal may be said, speaking broadly, to be com- 

 posed of two constituents : firstly, mineral charcoal ; 

 and, secondly, coal proper. The nature of the mineral 

 charcoal has long since been determined. Its structure 

 shows it to consist of the remains of the stems and 

 leaves of plants, reduced to little more than their carbon. 

 Again, some of the coal is made up of the crushed and 

 flattened bark, or outer coat, of the stems of plants, the 

 inner wood of which has completely decayed away. But 

 what I may term the "saccular matter" of the coal, 

 which, either in its primary or in its degraded form, con- 

 stitutes by far the greater part of all the bituminous 

 coals I have examined, is certainly not mineral charcoal ; 

 nor is its structure that of any stem or leaf. Hence its 

 real nature is, at first, by no means apparent, and has 

 been the subject of much discussion. 



The first person who threw any light upon the pro- 

 blem, as far as I have been able to discover, was the 

 well-known geologist. Professor Morris. It is now thirty- 

 four years since he carefully described and figured the 

 coin-shaped bodies, or larger sacs, as I have called them, 

 in a note appended to the famous paper " On the Coal- 

 brookdale Coal-Field/' published at that time, by the 

 present President of the Geological Society, Mr. Prest- 



