the seasons, of the trade winds, of the Gulf-stream are as much the results of the reaction between these inner activities and outward forces, as are the budding of the leaves in spring and their falling in autumn the effects of the interaction between the organization of a plant and the solar light and heat. And, as the study of the activities of the living being is called its physiology, so are these phenomena the subject-matter of an analogous telluric physiology, to which we sometimes give the name of meteorology, sometimes that of physical geography, sometimes that of geology. Again, the earth has a place in space and in time, and relations to other bodies in both these respects, which constitute its distribution. This subject is usually left to the astronomer ; but a knowledge of its broad outlines seems to me to be an essential constituent of the stock of geological ideas.
All that can be ascertained concerning the structure, succession of conditions, actions, and position in space, of the earth is the matter of fact of its natural history. But, as in biology, there remains the matter of reasoning from these facts to their causes, which is just as much science as the other, and indeed more ; and this constitutes geological aetiology.
Having regard to this general scheme of geological knowledge and thought, it is obvious that geological speculation may be, so to speak, anatomical and developmental speculation, so far as it relates to points of stratigraphical arrangement which are out of reach of direct observation ; or it may be physiological speculation, so far as it relates to undetermined problems relative to the activities of the earth ; or it may be distributional speculation, if it deals with modifications of the earth's place in space ; or, finally, it will be aetiological speculation, if it attempts to deduce the history of the world, as a whole, from the known properties of the matter of the earth in the conditions in which the earth has been placed.
For the purposes of the present discourse I may take this last to be what is meant by ' geological speculation.'
Now uniformitarianism, as we have seen, tends to ignore geological speculation in this sense altogether. The one point the catastrophists and the uniformitarians agreed upon when this Society was founded, was to ignore it. And you will find, if you look back into our records, that our revered fathers in geology plumed themselves a good deal upon the practical sense and wisdom of this proceeding. As a temporary measure, I do not presume to challenge its wisdom ; but in all organized bodies temporary changes are apt to produce permanent effects ; and as time has slipped by, altering all the conditions which may have made such mortification of the scientific flesh desirable, I think the effect of the stream of cold water which has steadily flowed over geological speculation within these walls, has been of doubtful beneficence.
The sort of geological speculation to which I am now referring (geological aetiology, in short) was created as a science by that famous philosopher Immanuel Kant, when, in 1755, he wrote his 'General Natural History and Theory of the Celestial Bodies ; or an attempt
