374 Analyses of Books. [May, 



simple or mixed rock, of a certain nature, and following it in 

 different places or in the different formations in which it occurs, 

 we examine at what epochs it has been deposited on the surface 

 of the globe, what are the minerals and rocks with which it is 

 associated, and what peculiarities it presents in each of these 

 epochs. This point of view is principally mineralogical, and 

 secondarUif geological : it is as productive as the first in general 

 results, and consequently as proper as it to discover the laws 

 which have presided at the structure of the earth, and at the 

 formation of the minerals that enter into its composition. 



" It is under this last point of view that I shall consider the 

 mineral which I have mentioned by the name Magnesite. 



" The following are the minerals to which I give this name. 

 I distinguish them in two principal series, which may one day 

 l)c separated into two species when we shall have observed 

 sufficiently essential characters to establish this distinction. 



" 1. Plastic magnesite (magnesite plastique), composed of 

 magnesia, silex, and water, without carbonic acid. 



" I here comprise the magnesite, so improperly named ecume 

 de Mer, that of the environs of Madrid, that of the environs of 

 Paris, that of Salinelle, department of the Gard, &c. 



" Serpentine might, from its composition, almost be referred 

 to tiiis species ; but it is distinguished from it by its mineralogi- 

 cal characters. 



<: 2. Effervescent magnesite (magnesite effervescente), essen- 

 tially composed of magnesia and carbonic acid, sometimes asso- 

 ciated with very variable proportions of silex and water. 



" We may refer to this division the magnesite of Hroubschitz, 

 in Moravia ; those of Piedmont, of the Isle of Elba, of Baumgar- 

 ten in Silesia, of Styria, 8cc. 



" Having made known, as far as it appears necessary, the 

 minerals 1 include under this name, I shall now describe the 

 position of the magnesite of the Paris basin, and present the 

 union of a few facts and observations in order to complete the 

 geognostic history of these minerals, the principal object of this 

 notice. 



Parisian Magnesite. 



** I first observed the presence of magnesite in rather exten- 

 sive beds at Coulommiers, 12 leagues to the E. of Paris, and 

 afterwards quite close to the latter town : I shall describe this 

 variety and the circumstances of its position with some detail, 

 as I shall afterwards employ it as a type of comparison with the 

 same mineral, found in other positions and in other places.* 



" The magnesite of Coulommiers, in the purest specimens, for 

 it is often mixed with other things, possess the following cha- 

 racters : — • 



* I am indebted to M. Merimee for the knowledge of this magnesite. He was 

 struck with the soapy unctuosity of a stone which he found at Coulommiers, and hav- 

 ing brought it to me, he put me in the way of discovering this mineral in the Paris 

 basin. 



