The experiments to be detailed in this paper, which chiefly go to establish properties of heat wholly unlooked for, or only suspected to exist, having been made entirely by means of an instrument of great delicacy—the thermo-multiplier of MM. Nobili and Melloni, I shall premise some account of its application to the investigation of some more familiar modes of action.

I propose in this memoir to methedically connect several desultory notices, which I had occasion to read during the last session of the Royal Society's meetings, relative to the Limestones of fresh-water origin in the neighbourhood of Edinburgh, belonging to the carboniferous group of rocks, and to the organic remains which they contain.

Hitherto, the limestones belonging to this older class of deposits have been considered as exclusively of marine origin. I had long since, however, been prepared to expect that a limestone of a fluviatile or fresh-water origin would, some time or other, be proved to exist. For, in judging from analogy, it would be unreasonable to presume, that, when fresh-water limestones appear in the rocks of every later epoch, they should meet with an exclusion in the carboniferous group. In entertaining, therefore, less confined views, I was not at all surprised to find them confirmed in a limestone near Edinburgh, which lately came under my examination,—I allude to that of Burdiehouse. It enclosed none of the marine shells, corallines, or encrinites to be found in the other limestones of the vicinity, but contained in the place of them, and in the greatest possible abundance, the various plants observable in our coal-fields. I also procured from it specimens of fish allied to such as are obtained from beds associated with coal. These facts indicated to me that I had at length found a fresh-water limestone belonging to the carboniferous group of rocks.

It is not my intention to enter into any detailed description of the external characters of the several interesting organic remains which are found imbedded in the limestone of Burdiehouse, that being a task which belongs to their distinguished discoverer Dr Hibbert.

As little do I mean to describe the geological relations of the limestone bed, that being equally the province of Dr Hibbert. It will be sufficient to state generally, that it forms one of the lowest members of the carboniferous group, being inferior in position even to the Encrinal mountain limestone of its immediate vicinity; and that besides its numerous animal remains, some of which will be mentioned in the sequel, it contains throughout its entire mass numerous impressions of land and fresh-water tropical plants.

It may be useful to distinguish some of the functions which water is already admitted to discharge in the constitution of hydrated salts.

Every amphigene ammoniacal salt contains an atom of water, and cannot exist without it. The state of combination of the water is peculiar, and has been represented by supposing that the elements of ammonia unite with the hydrogen of the water, and form a new compound radicle, to which the name Ammonium is given, while the oxygen of the water unites with this radicle, and produces oxide of ammonium. Hence nitrate of ammonia, in which there exist the elements of one atom of nitric acid, of ammonia, and of water, is viewed as anhydrous nitrate of the oxide of ammonium, and corresponds with nitre or the nitrate of the oxide of potassium. But it is not the object of this paper to discuss particularly the state of water in the ammoniacal salts.