of the Environs of /^ans, 4f 



We have the honour to present the class with the first of 

 'Hi series of mineralogical charts, in which each kind of soil 

 is coloured diifereutly. 



The sand is fawn-coloured; gypsum blue ; shelly lime 

 yellow; siliceous lime violet; chalk red colour; fresh- 

 water soil green streaked vviih white. We have here marked 

 in plain green, ihe worn or alluvial sands which have not 

 been tranquhly depo.sfted, but brought from other quarters 

 by currents; and m dark brown the j)eaiy soils formed along 

 the nvulets and round the pools of water. 



This <har', one of the principal results of our travels, is 

 complete in the coloured part, and we have only left im- 

 coloured that with which we are not ycl sufficiently ac- 

 quanited. 



Such are the great masses of which our district is com- 

 posed, and which form the different strata. But on sub- 

 dividing each stratum we may attain still greater precision, 

 and obtam still more rigorous mineralogical determinations, 

 which will give so many as ten distinct kinds of strata, of 

 which we shall now present a rapid enumeration. 



Article I» Formatio?i of Chalk, 



Chalk forms in the environs of Paris, as in almost all 

 those places where it has been observed, a mass in which 

 the straia are frequently so indistinct that we are almost 

 inclined to doubt whether it was formed by beds, if we did 

 not see these beds mterruptedby silex, which, by their per- 

 fectly horizontal position, their parallelism, their continui- 

 ties, and their frequency, uidicate successive and almost pe- 

 riodical depositions. 



Their respective distance varies according to the place : at 

 Meudon they are about two metres (7Sf Eng, inches) from 

 each other, and the space comprehended between any two 

 beds of silex does not contain any detached pieces of this 

 stone. At Bougival ihe beds are divided, and the silex is 

 much less abundant. 



The chalk which contains flints is not pure carbonated 

 lime: it contains, according to M. Bouillon Lagrange, about 

 0*1 1 of magnesia and 0*19 of" silex, the greatest part ofwhich 

 is in the state of sand, which we may separate by washing. 

 The fossils found in it are not numerous, in comparison 

 with those which we observe in the strata of coarse lime- 

 stone (which almost immediately cover the chalk), but they 

 are entirely diil'erent from these fossils, not only in the 

 gpccicg, but «vcn in the genera. 



On 



