Perhaps the best method which can be pursued is that recommended in the “Micrographic Dictionary,” which is as follows:--“The coal is macerated for about a week in a solution of carbonate of potash; at the end of that time it is possible to cut tolerably thin slices with a razor. These slices are then placed in a watch-glass with strong nitric acid, covered and gently heated; they soon turn brownish, then yellow, when the process must be arrested by dropping the whole into a saucer of cold water, else the coal would be dissolved. The slices thus treated appear of a darkish amber colour, very transparent, and exhibit the structure, when existing, most clearly. We have obtained longitudinal and transverse sections of coniferous wood from various coals in this way. The specimens are best preserved in _glycerine_ in cells; we find that spirit renders them opaque, and even Canada balsam has the same defect. Schulz states that he has brought out the cellulose reaction with iodine, in coal treated with nitric acid and chlorate of potash.” _Cannel-coal_ is so close and firm in its structure as to be much used instead of jet in the manufacture of ornaments: it takes a beautiful polish, and consequently presents the student with none but ordinary difficulties in getting sections of it. Its formation is somewhat different from that of coal, sometimes showing the transition very clearly. In _flint_ there are often found remains of sponges, shells, Diatomaceæ, &c.; but to show these well, sections must be cut and polished by the lathe and wheel of the lapidary, which the microscopic student seldom possesses. Thin chippings may, however, be made, which when steeped in turpentine and mounted in balsam, will frequently show these remains very well. _Teeth_ are very interesting objects to all microscopists, more especially to those who give much study to them; as the class of animal may very frequently be known from one solitary remaining tooth. To examine them thoroughly, it is necessary to cut sections of them; but this is rather difficult to perform well, and needs some experience. Some instructions, however, will at least lessen these difficulties, and we will now endeavour to give them.