69 
of Edinburgh, Session 1872-73. 
author, in offering the present solution of the enigma, ventures to 
hope that he has successfully grappled with the difficulty. Geolo- 
gists appear hitherto to have strangely overlooked, or at all events 
very much underrated, the solvent powers of water in effecting 
changes on strata during, inconceivably long periods of geological 
time, at great depths, and consequently under greater pressures 
and higher temperatures than are obtainable at the surface of the 
earth. The author contends that a just comprehension of the 
solvent action of water, slowly percolating through the strata 
during vast and nameless periods of time, and at pressures and 
temperatures of unknown intensity, will furnish the key to the 
elimination of the mineral from the carbonaceous matter which 
now constitutes our beds of coal. If carbon be not actually in- 
soluble, it may be assumed that it is practically so in relation to 
any known chemical action and as compared with the proportion- 
• ately easy solubility of the mineral ingredients, for the extension 
of which the present explanation is offered. Granting, therefore, 
the vast difference in degree of solubility, the immensity of the 
time since deposition, and the increased pressure and temperatures, 
with the incessant percolation of water through the strata, it is 
impossible to conceive any other result than the gradual washing 
out of the soluble from the insoluble constituents of any particular 
stratum. The different ingredients would disappear in the rotation 
of their degrees of solubility ; and, in the case of coal-beds, the 
separation and carrying away of the mineral or soluble ingredients 
in solution and the leaving the carbonaceous or insoluble matter 
behind, w r ould seem to be simply a question of time. The author 
touches upon several collateral features connected with the solvent 
action of water percolating through the strata, such as the deposi- 
tion of chemically-dissolved matter in other strata through which 
the water has to pass at a lessened temperature, and consequently 
with a diminished power of solution, the vast supplies of shell- 
forming substances constantly being carried into the sea, and thus 
maintaining a supply sufficient for the formation of myriads of 
shells, and whole islands and almost continents of coral reef; and, 
in conclusion, he submits that the solution now offered, besides 
doing away with the principal difficulty, will contribute to the 
elucidation of many other obscure points in geology. 
