Royal Academy of Sciences of Paris. 145 



deposits of the north of Europe are placed under the terrains tertiaires, 

 and over those known by the name of epiolithic (upper and middle 

 oolite), because they appear to form the upper part of the great 

 oolitic mass of the European Jurassic earth. The parts in the 

 south of France, in which they have appeared covered with 

 the terrains tertiaires, are the Landes, Medoe, the environs of 

 Bordeaux, and St. Paulet, near the Pont St. Esprit: those in which 

 the deposits under the chalk may be referred to the epiolithic group, 

 are much more numerous, chiefly near Rochefort and St. Jean 

 d'Angely. 



The principal difference of the physical structure of these chalk 

 formations from those of the north of Europe is, that they are 

 generally in oblique strata, which may be partly occasioned by the 

 elevation of the crystalline rocks, which constitute the Pyrenean 

 chain, lifting up part of the layers of chalk in greater or smaller 

 angles. The mineralogical characters of these deposits in the 

 south of France are, in some respects, similar and in others different 

 from those of the north of Europe ; but these differences are of 

 less importance, inasmuch as sedimentary rocks, to which these 

 belong, can never offer those decided and uniform mineralogical 

 characters which distinguish the crystallized rocks : for the latter 

 are formed under the influence of chemical composition, an invariable 

 principle of nature ; whereas the former may almost be said to be 

 mechanically constructed, under circumstances perpetually varying 

 and subjected to no certain rule. The chalk formations of the north, 

 of Europe are composed (commencing from the surface) of white 

 chalk, a grayish and friable rock called tufous chalk, a sandy rock, 

 filled with green particles, and called glauconie crayeuse, and fre- 

 quently of a sandy and ferruginous rock. Under this last rock there 

 has been observed in England, and particularly in Sussex, a remark- 

 able deposit of shells and fossil animals of the lake and river species : 

 this is called the groupe Veldien. Sand, tolerably pure freestone, 

 some metallic combinations of hydroxidated iron, and pyrites, 

 are also observed in these earths. M. Dufresnoy has ascer- 

 tained that the greater part of these substances are found in the 

 chalk deposits of the south of France ; and particularly that the 

 groupe Veldien, supposed to be peculiar to Sussex, exists at the base 

 of the Montague d'Angouleme and at La Grasse. Although this 

 deposit is less distinct in France than in England, it is easily 

 recognized by the argilo-calcareous nature of its rock, by its 

 position, and by its lacustrine shells (melanie, paludinis). The 

 great difference in the mineralogical character of these deposits 

 from those of the north of Europe is the almost total absence 

 of white chalk, which has either never been deposited or else 

 been carried off. The formation generally begins with the 

 tufous chalk. Another very remarkable difference is, that in 

 some cases (particularly at St. Froult, near Rochefort), they con- 

 tain masses of gypsum, with its accompanying sulphur: by the 

 VOL, II. Aua. 1831. L 



