650 Proceedings of the Royal Society 
Thus every characteristic quality which distinguishes mineral 
coal from ordinary decomposed vegetable substances has now been 
considered, and, I think, provided for in the exercise of these its 
newly discovered properties of absorption and solubility. 
Whether a slight elevation of temperature is necessary or no to 
assist in educing those members of the coal series, very far removed 
from the primary material, it is certain it would greatly facilitate 
the mineralisation of these deposits, but in either case it is the 
presence of water which, besides initiating the commencement of 
the required changes, allows of them being carried to the farthest 
point, by bringing the particles of the solid substances within reach 
of each other’s affinities, thus determining the production of new 
combinations more insoluble, more carbonaceous, and more easily 
absorbed ; and these being deposited as they were formed slowly^ the 
hardness, coherence, and compactness of the deposit are ensured. 
IV. Poyidar theory^ explaining the Physical Properties of Coal 
considered. 
As I have purposely avoided all along any reference to other 
theories respecting the formation of coal, in order that no external 
influence should be brought to secure favour for the views here 
propounded from prematurely showing up their deficiencies, pre- 
ferring rather that they shoiild stand thus long on their own merits 
uncontrasted with those of others. I hope now to be allowed to 
state a few objections — objections so obvious and so serious that 
they will have frequently occurred to the mind of the inquirer. 
The principal agencies hitherto supposed to be involved in the 
formation of coal are decomposition, pressure, and heat. In regard 
to decomposition, important and indeed essential as it is to the 
formation of coal, it is still possible to overstate its influence. 
Taken by itself, it is obvious it cannot increase the hardness of 
coal. It is the property of decay rather to reduce than to jcrease 
the hardness of minerals, the most compact of which are thus 
modified, and especially should this be apparent in coal where it 
involves a positive loss of substance. This is well exemplified in 
the case of wood which has suffered the “ dry rot, here, from the 
absence of water in sufficient quantity, there has been no recom- 
position ” of the decomposed matters ; hence even the colour is 
