The making of rock sections is certainly different to the cutting of plant or animal sections. It is a laborious business as the enthusiast will find to his cost. The professional makers of rock sections have special grindstones or lathes for the purpose and, even so, the process is not rapid. The amateur must needs do all his preparation by hand. The requirements, in addition to the piece of rock of which we require a section, are a small square of plate glass, some Canada Balsam, emery powder of various grades and an unlimited stock of patience. If possible we choose a piece of rock with one side as nearly as possible flat; this is merely to save labour; the piece of rock should be roughly about half-an-inch square. As a start we rub the flattest side in a mixture, practically a paste, of coarse emery powder and water. As a matter of fact, we may keep the piece of rock in our pocket and grind it when occasion offers on a flat stone wall or on any surface that will assist in producing a flat surface. When we have ground our surface flat and smooth, we finish it off with fine emery powder and may then polish it with jeweller’s rouge. So much for the first side and, if we do not cry enough at this period, we may proceed to the grinding of the other side. Taking our slab of plate glass, we fasten the polished side of our piece of rock to it by means of Canada Balsam, then we may rest for a few days while the Balsam sets. As soon as the rock is firmly fixed to the glass we proceed as before, but in this case the final grinding and polishing must be very carefully carried out. Towards the end of the operation our original lump of rock will be reduced to the thinness of a cover slip and to its fragility. Having given the finishing touches with jeweller’s rouge, we put the glass, with its attached rock section into a bottle of xylol (to be obtained from any chemist). The xylol dissolves the Canada Balsam and the rock section falls from its support. A further washing in clean xylol should be given and then the section is ready for mounting, which is best done in Canada Balsam. The section may be carefully fixed to the slide with a drop of Balsam or it may be covered with a cover slip, in the usual manner. In our concluding chapter we give hints on slide making and addresses of firms who supply slides. Our advice in that chapter is to prepare one’s own slides where possible; in the case of rock sections, however, we must change our advice, only the microscopist of unlimited leisure can find time to make his own slides.