But besides the power or effect of subterraneous heat in bodies which are unorganised, and without system, in the construction of their different parts, we have to investigate the proper purpose of this great agent in the system of this world, which may be considered as a species of organised body. Here, therefore, final causes are to be brought into view, as well as those which are efficient. Now, in a subject involved with so much obscurity, as must be for us the internal regions of the globe, the consideration of efficient and final causes may contribute mutually to each others evidence, when separately the investigation of either might be thought unsatisfactory or insufficient. So far it seemed necessary to premise with regard to the great mineral power which we are to employ as an agent in the system of this earth; and it may be now observed, that it is in the proper relation of this power of heat and the fluidity or softness of bodies, as cause and effect, that we are to find a physical principle or argument for detecting those false theories of the earth that have been only imagined, and not properly founded on fact or observation. It is also by means of this principle, that we shall be enabled to form a true theory of the mineral region, in generalising particular effects to a common cause. Let us now proceed in endeavouring to decide this important question, viz. By what active principle is it, that the present state of things, which we observe in the strata of the earth, a state so very different from that in which those bodies had been formed originally, has been brought about? Two causes have been now proposed for the consolidating of loose materials which had been in an incoherent state; these are, on the one hand, fire; or, on the other, water, as the means of bringing about that event. We are, therefore, to consider well, what may be the consequences of consolidation by the one or other of those agents; and what may be the respective powers of those agents with respect to this operation. If we are not informed in this branch of science, we may gaze without instruction upon the most convincing proofs of what we want to attain. If our knowledge is imperfect, we may form erroneous principles, and deceive ourselves in reasoning with regard to those works of nature, which are wisely calculated for our instruction.