If an organised body is not in the situation and circumstances best adapted to its sustenance and propagation, then, in conceiving an indefinite variety among the individuals of that species, we must be assured, that, on the one hand, those which depart most from the best adapted constitution, will be most liable to perish, while, on the other hand, those organised bodies, which most approach to the best constitution for the present circumstances, will be best adapted to continue, in preserving themselves and multiplying the individuals of their race.
Source: An Investigation into the Principles of Knowledge (1794)
Note: This passage suggests that more than than 50 years before the publication of On the Origin of Species, Hutton anticipated Darwin's theory of natural selection.
The past history of our globe must be explained by what can be seen to be happening now. No powers are to be employed that are not natural to the globe, no action to be admitted except those of which we know the principle.
Source: Theory of the Earth (Paper, published in Transactions of the Royal Society of Edinburgh in 1785)
We find no vestige of a beginning - no prospect of an end.
Hutton published a landmark treatise, Theory of the Earth, in which he set forth the principle of uniformitarianism: the present is the key to the past. He proposed the same processes of erosion, weathering, uplift and sedimentation that are sculpting the land today have been at work throughout the eons. ...In Hutton's day, uniformitarianism was a refutation of theories that called upon catastrophic events like the biblical flood to explain the way the world looked. But even as these deux ex machina theories fell to the wayside, Hutton's ideas continued to hold sway...
In a letter to Sir John Hall, he says that he was become very fond of studying the surface of the earth, and was looking with anxious curiosity into every pit, or ditch, or bed of a river that fell in his way; "and that if he did not always avoid the fate of Thales, his misfortune was certainly not owing to the same cause." This letter is from Yarmouth; it has no date, but it is plain from circumstances that it must have been written in 1753.
Among other advantages... we must reckon that of being able to enjoy, with less interruption, the society of his literary friends, among whom were Dr Black, Mr Russel, professor of Natural Philosophy, Professor Adam Ferguson, Sir George Clerk... his brother Mr Clerk of Elden, Dr James Lind... and several others. Employed in maturing his views, and studying nature with unwearied application, he now passed his time most usefully and agreeably to himself, but in silence and obscurity with respect to the world. He was, perhaps, in the most enviable situation in which a man of science can be placed. He was in the midst of a literary society of men of the first abilities, to all of whom he was peculiarly acceptable, as bringing along with him a vast fund of information and originality, combined with that gayety and animation which so rarely accompany the profounder attainments of science. Free from the interruption of professional avocations, he enjoyed the entire command of his own time, and had sufficient energy of mind to afford himself continual occupation.
A good deal of his leisure was now employed in the prosecution of chemical experiments. In one of these experiments... which I have heard of from Dr Black, he discovered that mineral alkali is contained in zeolite. On boiling the gelatinous substance obtained from combining that fossil with muriatic acid, he found that, after evaporation, sea-salt was formed. ...from circumstances... it was earlier than 1772. It is, if I mistake not, the first instance of an alkali being discovered in a stony body.
From the date... when he was yet a very young man, and making excursions on foot through the different counties of England, till that which we are now arrived at, a period of about thirty years, he had never ceased to study the natural history of the globe, with a view of ascertaining the changes that have taken place on its surface, and of discovering the causes by which they have been produced.
Few men have entered with better preparation on the arduous task of investigating the true theory of the earth.
He was one of those who are much more delighted with the contemplation of truth, than with the praise of having discovered it.
The object of Dr Hutton was not, like that of most other theorists, to explain the first origin of things. He was too well skilled in the rules of sound philosophy for such an attempt; and he accordingly confined his speculations to those changes which terrestrial bodies have undergone since the establishment of the present order, in as far as distinct marks of such changes are now to be discovered.
The first general fact which he has remarked is, that by far the greater part of the bodies which compose the exterior crust of our globe, bear the marks of being formed out of the materials of mineral or organized bodies, of more ancient date. The spoils or the wreck of an older world are every where visible in the present, and, though not found in every piece of rock, they are diffused so generally as to leave no doubt that the strata which now compose our continents are all formed out of strata more ancient than themselves.
The present rocks, with the exceptions of such as are not stratified, having all existed in the form of loose materials collected at the bottom of the sea, must have been consolidated and converted into stone by virtue of some very powerful and general agent. The consolidating cause which he points out is subterraneous heat, and he has removed the objections to this hypothesis by the introduction of a principle new and peculiar to himself. This principle is the compression which must have prevailed in that region where the consolidation of mineral substances was accomplished. Under the weight of a superincumbent ocean, heat, however intense, might be unable to volatilize any part of those substances which, at the surface, and under the lighter pressure of our atmosphere, it can entirely consume. The same pressure, by forcing those substances to remain united, which at the surface are easily separated, might occasion the fusion of some bodies which in our fires are only calcined. Hence the objections that are so strong and unanswerable, when opposed to the theory of volcanic fire, as usually laid down, have no force at all against Dr Hutton's theory; and hence we are to consider this theory as hardly less distinguished from the hypothesis of the Vulcanists, in the usual sense of that appellation than it is from that of the Neptunists or the disciples of Werner.
The third general fact on which this theory is founded, is, that the stratified rocks, instead of being either horizontal, or nearly so, as they no doubt were originally, are now found possessing all degrees of elevation, and some of them even perpendicular to the horizon; to which we must add, that those strata which were once at the bottom of the sea are now raised up, many of them several thousand feet above its surface. ...This force, which has burst in pieces the solid pavement on which the ocean rests, and has raised up rocks from the bottom of the sea, into mountains... exceeds any which we see actually exerted, but seems to come nearer to the cause of the volcano or the earthquake than to any other, of which the effects are directly observed. The immense disturbance, therefore, of the strata, is in this theory ascribed to heat acting with an expansive power, and elevating those rocks which it had before consolidated.
Among the marks of disturbance in which the mineral kingdom abounds, those great breaches among rocks, which are filled with materials different from the rock on either side, are among the most conspicuous. These are the veins, and comprehend, not only the metallic veins, but also those of whinstone, of porphyry, and of granite, all of them substances more or less crystallized, and none of them containing the remains of organized bodies. ...The materials of all these veins Dr Hutton concludes to have been melted by subterraneous heat, and, while in fusion, injected among the fissures and openings of rocks already formed, but thus disturbed, and moved from their original place.
Hutton was... no narrow specialist, wrapped up in the pursuit of one circumscribed section of human inquiry. His mind ranged far and wide over many departments of knowledge. ...His pleasure in every outward step made by science and philosophy showed itself in the most lively demonstrations.
The world... might have had still a long time to wait for the appearance of his dissertation, had it not been for the interest he took in the foundation of the Royal Society of Edinburgh... At one of the early meetings of this Society he communicated a concise account of his Theory of the Earth., which appeared in the first volume of the Transactions. This essay was afterwards expanded...
Dr. Hutton... was highly pleased with appearances that set in so clear a light the different formations of the parts which compose the exterior crust of the earth... On us who saw these phenomena for the first time, the impression made will not easily be forgotten. ...The mind seemed to grow giddy by looking so far into the abbys of time; and while we listened with earnestness and admiration to the philosopher who was now unfolding to us the order and series of these wonderful events, we became sensible how much further reason may sometimes go than imagination can venture to follow.
His character was distinguished by its transparent simplicity, its frank openness, its absence of all that was little or selfish, and its overflowing enthusiasm and vivacity.
Though his partnership in the chemical work brought him considerable wealth, it made no difference in the quiet unostentatious life of a philosopher, which he had led ever since he settled in Edinburgh.
Hutton's claim to rank high among the founders of geology rests on no wide series of writings, like those which Von Buch poured forth so copiously for more than two generations. Nor was it proclaimed by a host of devoted pupils, like those who spread abroad the fame of Werner. It is based, so far at least as geology is concerned, on one single work, and on the elucidations of two friends and disciples.