letting it to advantage, he availed himself of it. About the year 1768 he left Berwickshire entirely, and became resident in Edinburgh, giving his undivided attention, from that time, to scientific pursuits.

Among other advantages which resulted to him from this change of residence, we must reckon that of being able to enjoy, with less interruption, the society of his literary friends, among whom were Dr Black, Mr Russell Professor of Natural Philosophy, Professor Adam Fergusson, Sir George Clerk, already mentioned, his brother Mr Clerk of Elden, Dr James Lind, now of Windsor, 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 gaiety 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 he has no where mentioned himself, but 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. Dr Black did not recollect exactly the date of this experiment, but from circumstances judged that it was earlier than 1772. It is, if I mistake not, the first instance of an alkali being discovered in a stony body. The experiments of M. Klaproth and Dr Kennedy have confirmed this conclusion, and led to others of the same kind.

In 1774 he made a tour through part of England and Wales, of which I find no memorandum whatever among his papers. I know, however,

that at this time he visited the salt-mines in Cheshire, and made the curious observation of the concentric circles marked on the roof of these mines, to which he has referred in his Theory of the Earth, as affording a proof that the salt rock was not formed from mere aqueous deposition. His friend Mr Watt of Birmingham accompanied him in his visit to the mines.

One

It was after returning to Birmingham from Cheshire, that he set out on the tour into Wales. of the objects of this tour, as I learnt from himself,

was to discover the origin of the hard gravel of granulated quartz, which is found in such vast abundance in the soil about Birmingham, and indeed over a great tract of the central part of England. This gravel is so unlike that which belongs to a country of secondary formation, that it very much excited his curiosity; and his present journey was undertaken with a view to find out whether, among the primitive mountains of Wales, there were any that might be supposed to have furnished the materials of it. In Wales, however, he saw none that could, with any probability, be supposed to have done so; and he was equally unsuccessful in all the other parts he visited, till returning, at a small distance from Birmingham, the place from whence he had set out, he found a rock of the very kind which he had been in search of. It belongs to a body of strata apparently primary, which break out between Broomsgrove and Birmingham, and have all the characters of the indurated gravel in question. If, however, they have furnished the materials of that gravel, it seems probable that it has been through the medium of the red sandstone, which abounds in those countries. *

In 1777 Dr Hutton's first publication was given to the world, viz. a small pamphlet, entitled, Con

Illustrations of the Huttonian Theory, p. 375.

This little work, an oc

siderations on the Nature, Quality, and Distinctions of Coal and Culm. tavo pamphlet of thirty-seven pages, was occasioned by a question that had arisen, Whether the small coal of Scotland is the same with the culm of England? and, Whether, of course, like the latter, it is entitled, when carried coastwise, to an exemption from the duty on coal? Some of the small coal from the Frith of Forth, which had been carried to the northern counties for the purpose of burning lime, had been considered by the revenue officers as liable to the same duty with other coal, while the proprietors contended that it ought only to pay the lighter duty levied on culm. This was warmly disputed; and, after occupying for some time the attention of the Board of Customs in Scotland, was at last brought before the Privy Council.

Dr Hutton's pamphlet was intended to supply the information necessary for forming a judgment on this question. It is very ingenious and satisfactory, though perhaps, considering the purpose for which it was written, it is on too scientific a plan, and conducted too strictly according to the rules of philosophical analysis. It proves that culm is the small, or refuse, of the infusible, or stone coal, such as that of Scotland for the most part is; that the small of the fusible coal, by caking or uniting together, becomes equally serviceable with the large

coal; whereas the small of the infusible, by running down like loose sand, cannot be made to burn in the ordinary way, and is useful but for few purposes, so that it has been properly exempted from the usual duty on coal. A criterion is also pointed out for determining when small coal is to be regarded as culm, and when it may be considered as coal;-if, when a handful of it is thrown into a red-hot shovel, the pieces burn without melting down or running together, it decidedly belongs to the former.

. In the conclusion, an exemption from duty was obtained for the small coal of Scotland, when carried coastwise, and this regulation was owing in a great degree to the satisfactory information contained in Dr Hutton's pamphlet. It was a step, also, toward the entire abolition of those injudicious duties which had been so long levied on coal, when carried by sea beyond a certain distance from its native place. This abolition happened several years after the period we are speaking of, much to the benefit of the country, and to the credit of the administration under which it took place.

As Dr Hutton always took a warm interest in whatever concerned the advancement of the arts, particularly in his native country, he entered with great zeal into the project of an internal navigation between the Friths of Forth and Clyde. The comparative merit of the different plans, according to