Many of the Cainozoic fossils from the shelly sands and clays are extremely delicate, owing in some cases to their being imperfectly preserved, seeing that they frequently contain in their shell-structure layers of the unstable form of carbonate of lime called aragonite. Fossils containing aragonite are:--Calcareous Sponges; Corals; Bivalved shells, except Oysters, Pectens, and the outer layer of _Spondylus_, _Pinna_, and _Mytilus_; Gasteropods (with a few exceptions); and Cephalopods. In some of these, however, a transformation of the aragonite into calcite enables the fossil to be permanently preserved. The delicate fossils referred to should be dipped in weak glue or gelatine and left to dry; after which their final cleaning can be done with the aid of a little warm water and a soft brush. Certain of the clays and mudstones, both of Cainozoic and Jurassic ages which show remains of plants, such as leaves and fern fronds, are often best treated with a thin surface layer of paper varnish, before they lose the natural moisture of the rock; for when they become perfectly dry the thin carbonaceous film representing the original leaf-substance peels off, and the fossil is consequently destroyed. A method of treatment for Cainozoic leaves, by dipping them in warm vaseline and brushing off the superfluous material, has been described by Mr. H. Deane. =Storing Fossils for Reference.--= Fossils specimens are generally best displayed in cardboard trays; or if thin wooden paper-covered tablets are used, say of about 3-16in. thickness and cut to proportionate sizes, the fossils should be held in place by pins for easy removal, unless more than one example can be shown together, exhibiting all aspects, when they can be secured to the tablet by a touch of seccotine. The smaller shells may be displayed in glass topped boxes, which in turn may be stuck down to tablets or placed in trays. INDEX.