In operating on siliceous objects, I have found soap and water quite as speedy and efficacious as oil, which is generally used; while calcareous fossils must be slit by a solution of common soda in water. This solution of soda, if made too strong, softens the india-rubber on the face of the pneumatic chuck, and renders a new piece necessary; but if care is taken to keep the solution of moderate strength, one piece of india-rubber may last for six months. The thinner and flatter it becomes, the better hold the glass takes, until a puncture occurs in the outer portion, and a new piece is rendered necessary. The polishing of the section is the last operation. This is performed in various ways, according to the material of which the organism is composed. If siliceous, a _lap_ of tin is to be used, about the same size as the grinding _lap_. Having turned the face smooth and flat, a series of very fine notches are to be made all over the surface. This operation is accomplished by holding the edge of an old dinner-knife almost perpendicular to the surface of the _lap_ while rotating; this produces a series of _criddles_, or slight asperities, which detain the polishing substance. The polishing substance used on the tin lap is technically called lapidaries' rot-stone, and is applied by slightly moistening the mass, and pressing it firmly against the polisher, care being taken to scrape off the outer surface, which often contains grit. The specimen is then to be pressed with some degree of force against the revolving tin _lap_ or polisher, carefully changing the plane of action, by moving the specimen in various directions over the surface. To polish calcareous objects, another method must be adopted as follows:-- A _lap_ or disc of willow wood is to be adapted to the spindle of the lathe, three inches in thickness, and about the diameter of the other laps (10 inches), the axis of the wood being parallel to the spindle of the lathe, that is, the acting surface of the wood is the end of the fibres, the section being transverse.