30 M. D'Omalius D'Halloy on 



manner as the other sandy rocks, whose local formation is 

 now well demonstrated, as well by alternations with other 

 rocks, as by the fossils they contain. 



The first idea that this hypothesis presents, is to consider 

 the sands of the northern Sologne as belonging to the ancient 

 chalk formation, as also those of the southern part of the 

 same region, of la Touraine, of le Perche, &c. The exist- 

 ence, in these last, of large grained beds, resembling the 

 sand between the Loire and the Saudre, supports this opinion. 

 But, on the other hand, the presence of these sands on the 

 freshwater limestone of the borders of the Loire and the 

 Gatinais, that of small patches of analogous sands, on the 

 same limestone, in other places nearer Paris, as at Etampes, 

 at Rambouillet, &c.; lastly, certain relations that they bear 

 to the millstone formation, might give rise to the idea of 

 their being the last term of the second freshwater formation 

 of the Paris basin, such as Messrs. Cuvier and Brongniart 

 have considered the sands to be that occur on the top of the 

 hills of Longjumeau.* 



I confess that 1 am still at a loss to decide between these 

 two opinions, and if I had not comprehended the countries 

 between the Loire and the Saudre in the Paris basin, I had 

 determined, for want of geological reasons, from the con- 

 sideration of physical geography alone, not to dismember so 

 natural a region as la Sologne. It is proper nevertheless to 

 remark in this respect, that in the hypothesis that all the 

 sands of this country belong to the ancient chalk, it is very 

 easy to conceive their extension over the freshwater forma- 

 tion ; for this deposit of moveable matter;, situated precisely 

 at the opening of the great water courses descending from 

 the mountains of Auvergne, ought to be more disturbed by 

 the waters than those which occur under different circum- 

 stances ; and some grand catastrophes, such, for instance, as 

 that which has overwhelmed the animals of the marl and 

 gravel, might be sufficient to throw a part of these sands over 

 on the little elevated edge of the freshwater limestone 



* Min. Geo. of the Environs of Paris, p. 55. 



