At the base of the _Argile Plastique_ of France is a conglomerate of chalk and of divers calcareous substances, in which have been found at Bas-Meudon some remains of Reptiles, Turtles, Crocodiles, Mammals, and, more lately, those of a large Bird, exceeding the Ostrich in size, the _Gastornis_, which Professor Owen classes among the wading rather than among aquatic birds. In the Soissonnais there is found, at the same horizon, a great mass of lignite, enclosing some shells and bones of the most ancient Pachyderm yet discovered, the _Coryphodon_, which resembles at once both the Anoplotherium and the Pig. The _Sables Inférieurs_, or Bracheux Sands, form a marine bed of great thickness near Beauvais; they are principally sands, but include beds of calciferous clay and banks of shelly sandstone, and are considered to be older than the plastic clay and lignite, and to correspond with the Thanet Sands of England. They are rich in shells, including many Nummulites. At La Fère, in the Department of the Aisne, a fossil skull of _Arctocyon primævus_, supposed to be related both to the Bear and to the Kinkajou, and to be the oldest known Tertiary Mammal, was found in a deposit of this age. This series seems to have been formed chiefly in fresh water. The _Calcaire grossier_, consisting of marine limestones of various kinds, and with a coarse, sometimes compact, grain, is suitable for mason-work. These deposits, which form the most characteristic member of the Paris basin, naturally divide themselves into three groups of strata, characterised, the first, by _Nummulites_; the second by _Miliolites_; and the third or upper beds by _Cerithia_. The beds are also sometimes named Nummulite limestone, Miliolite limestone, and Cerithium limestone. Above these a great mass, generally sandy, is developed. It is marine at the base, and there are indications of brackish water in its upper parts; it is called Beauchamp Sandstone, or Sables Moyens (_Grès de Beauchamp_). These sands are very rich in shells. The _siliceous limestone_, or lower travertin, is a compact siliceous limestone extending over a wide area, and resembles a precipitate from mineral waters. The _gypseous_ formation consists of a long series of marly and argillaceous beds, of a greyish, green, or white colour, in the intervals between which a thick deposit of gypsum, or sulphate of lime, is intercalated. This gypsum bed is found in its greatest thickness in France at Montmartre and Pantin near Paris. The formation of this gypsum is probably due to the action of free sulphuric acid upon the carbonate of lime of the formation; the sulphuric acid itself being produced by the transformation of the gaseous masses of sulphuretted hydrogen emanating from volcanic vents, into that acid, by the action of air and water. It was, as we have already said, in the gypsum-quarries of Montmartre that the numerous bones of Palæotherium and Anoplotherium were found. It is exclusively at this horizon that we