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Show 206 MIOCENE PEltlOD. [Ch. XV, n.u m magnum, .utwa stodon angustiden• s, Hippopotam• us major, an d H . mt·n u t us, Rhinoceros leptorhmus, and R. mtnutus, Ta~ pt·r gt·g as, Anthrac·o therium (small species),. Su.~, Equus (sma. ll speci·e s ) , c er v•.•. s ' and an u. nd.e te.r mined species of the. Rodentia. The first species on this hst IS common to the Paris gypsum, and is therefore an example of a land quadruped common to the Miocene and Eocene formations, an exception perfectly in harmony with the results obtained from the study of fossil shells*· Basin of the Gironde and district of the Landes.-A great extent of country between the Pyrenees and the Gironde is overspread by tertiary deposits which have been more particularly studied in the environs of Bordeaux an~ Dax, from whence about 600 species of shells have been obtamed. These shells belong to the same type as those of Touraine.-See Appendix l.t Most of the beds near Dax, whence these shells are procured, consist of incoherent quartzose sand, mixed for the most part with calcareous matter, which has often bound together the sand into concretionary nodules. A great abundance of fluviatile shells occur in many places intermixed with the marine ; and in some localities microscopic shel1s are in great profusion. The tertiary deposits in this part of France are often very inconstant in their mineralogical .character, yet admit generally of being arranged in four groups, which are enumerated in the explanation of diagram No. 51. In some places the united thickness of these groups is considerable, but in the country between the Pyrenees and the valley of the Adour around Dax, the disturbed secondary rocks * For further details respecting the basin of the Loire, see M. Desnoyers, Ann, des Sci. Nat., tome xvi. pp. 171 and 402, where full references to other authors are given. t M. de Basterot has given a description of more than 300 shells of Bordeaux and Dax, and figures of the greater number of them. Mem. de la Soc. d'Hist, Nat. de Paris, tome ii, Ch.XV.] STRATA NEAR DAX. 207 are often covered by a thin pellicle only of tertiary strata, which rests horizontally on the chalk and does not always conceal it. Adour R. Luy R. Puy Arzet. No. 51. ~--=~nz9~ Tertiary strata overlying chalk in tl~e environs of Da:c. a, Siliceous sand without shells. c, Sand and marl with shells. b, Gravel. d, Blue marl with shells. \ E, Chalk and volcanic tuff. In the valleys of the Adour and Luy, sections of all the members of the tertiary series are laid open, but the lowest blue marl, which is sometimes 200 feet thick, is not often penetrated. On the banks of the Luy, however, to the south of Dax, the subjacent white chalk is exposed in inclined and vertical strata. In the hill called Puy Arzet the chalk, characterized by its peculiar fossils, is accompanied by beds of volcanic tuff, which are conformable to it, and which may be considered as the product of submarine eruptions which took place in the sea wherein the chalk was formed. About a mile west of Orthes, in the Bas Pyrenees, the blue marl is seen to extend to the borders of the tertiary formation, and rises to the height probably of six or seven hundred feet. In that locality many of the marine Miocene shells preserve their original colours. This marl is covered by a considerable thickness of ferruginous gravel, which seems to increase in volume near the borders of the tertiary basin on the side of the Pyrenees. In an opposite direction, to the north of Dax, the shel1y sands often pass into calcareous sandstone, in which there are merely the casts of shells as at Carcares, and into a shelJy breccia resembling some rocks of recent origin which I have received from the coral reefs of the Bermudas. Fres~water limestone at Saucats.-Associated with the Miocene strata near Dordeaux, at a place caUed Saucats, is a |