14. Such are the more obvious, but I think unanswerable objections, that may be urged against the aqueous consolidation of the strata. It is true, that stony concretions, some of them much indurated, are formed in the humid way under our eyes. Very particular conditions, however, are required for that purpose, and conditions such as can hardly have existed at the bottom of the sea. First. The water must dissolve the substance of which the concretion is to be formed, as it actually does in the case of calcareous, and in certain circumstances, in that of siliceous, earth. Secondly. It must be separated from that substance, as by evaporation, or by a combination of the matter dissolved with some third substance, to which it has a greater affinity than to water, so as to form with it an insoluble compound. Lastly, the water that is deprived of its solution must be carried off, and more of that which contains the solution must be supplied, as sometimes happens where water runs in a stream, or drops from the roof of a cavern. The two last conditions are peculiarly inapplicable to the bottom of the sea, where the state of the surrounding fluid would neither permit the water that was deprived of its solution from being drawn off, nor that which contained the solution from succeeding it. It is further to be observed, that the consolidation of stalactitical concretions, that is, the filling up of their pores, is always imperfect, and is brought about by the repeated action of the fluid running through the porous mass, and continuing to deposit there some of the matter it holds in solution. This, which is properly infiltration, is incompatible with the nature of a fluid, either nearly, or altogether quiescent. 15. In order to judge whether objections of equal weight can be opposed to the hypothesis of igneous consolidation, we must attend to a very important remark, first made by Dr Hutton, and applied with wonderful success to explain the most mysterious phenomena of the mineral kingdom. It is certain, that the effects of fire on bodies vary with the circumstances under which it is applied to them, and, therefore, a considerable allowance must be made, if we would compare the operation of that element when it consolidated the strata, with the results of our daily experience. The materials of the strata were disposed, as we have already seen, loose and unconnected, at the bottom of the sea; that is, even on the most moderate estimation, at the depth of several miles under its surface. At this depth, and under the pressure of a column of water of so great a height, the action of heat would differ much from that which we observe here upon the surface; and, though our experience does not enable us to compute with accuracy the amount of this difference, it nevertheless points out the direction in which it must lie, and even marks certain limits to which it would probably extend.