1824.] De la Beche's Selection of Geological Memoirs. 375 



" Its masses are soft, smooth to the touch without being 

 unctuous ; its powder is rather hard. 



" It easily absorbs water and swells out considerably, becomes 

 slightly translucent, and forms a short soft paste, resembling 



jelly. 



" It does not effervesce with acids. , 



" Exposed to the action of a porcelain furnace (at 140° of 

 Wedgevvood), it hardens, exfoliates a little, but does not suffer 

 any other alteration ; it does not show the slightest trace of 

 fusion, either in its thin pieces or on the surface ; it however 

 becomes rough to the touch, and hard enough to scratch steel. 



" M. Berthier has analyzed this magnesite, chosen from the 

 purest masses, and has found the following ingredients : — 



Magnesia 24-0 



Silex 54-0 



Water 20-0 



Alumine 01-4 



99-4 



" The magnesite of Coulommiers occurs in masses, which, 

 by their schistose structure and thinness, show they belong 

 to thin beds. 



" Its colour is whitish, most commonly pale grey ; it has often 

 a roseate tint, but it loses that and its grey colour in the fire. 

 It is associated with brownish and reddish chert (silex corne) of 

 a very scaly fracture ; it is intimately united with it, and pene- 

 trates into all its cavities, and even into its mass ; it is also very 

 frequently associated with marly limestone, and then effervesces 

 and becomes partly fusible. 



" This magnesite occurs in thin beds, interposed between beds 

 of marly limestone and calcareous marl, near Coulommiers, on 

 the right of the road, entering the town on the Paris side, in a 

 small hill having a north and south direction, and which having 

 been cut to form a canal, exposes its interior structure and the 

 following series of rocks, beginning with the uppermost. 



" L A bed, composed of siliceous limestone, the middle of 

 which is of white and cellular chert (silex corne), and the com- 

 pact limestone mass filled by small shells scarcely determinable, 

 and by larger shells, such as Limneus longiscatus, cyclostoma 

 mumia, &c. 



" 2. This bed rests on a bed of very irregular thickness, of a 

 greyish fissile earth, resembling clayey marl, and which has been 

 recognised to be an impure magnesite, i. e. mixed with calcare- 

 ous mail. 



" 3. Then follows a bed of soft and friable calcareous marl, 

 containing another small bed of magnesite. 



" 4. A bed of calcareous marl without silex, beneath which is 

 another small bed of brown impure magnesite. 



