Magnesile of the Paris Basin, Sfc. 285 



ttiass ; it is also very frequently associated with marly lime- 

 stone, and then effervesces and becomes partly fusible. 



This magnesite occurs in thin beds, interposed between 

 beds of marly limestone and calcareous marl, near Coulom- 

 miers, on the right of the road, entering the town on the 

 Paris sidCj in a small hill having a north and south direc- 

 tion, and which having been cut to form a canal, exposes its 

 interior structure and the following series of rocks, beginning 

 with the uppermost, (pi. 10, fig. 1.) 



1. A bed A, composed of siliceous limestone, the middle 

 of which is of white and cellular chert (silex come), and the 

 compact limestone mass filled by small shells scarcely deter- 

 minable, and by larger shells, such as Limneus longiscatus, 

 cyclostoma mumia, &c. 



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

 of a greyish fissile earth, resembling clayey marl, and which 

 has been recognised to be an impure magnesite (m.), i. e. 

 mixed with calcareous marl. 



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

 containing another small bed of magnesite (m). 



4. A bed of calcareous marl without silex, beneath whieh 

 is another small bed of brown impure magnesite. 



5. A thick bed of white calcareous marl D, subdivided 

 into many strata by marl beds, and by a bed of zoned chert 

 (silex corne zonaire), almost jaspic, without either shells or 

 magnesite. 



6. A bed E about two decimetres thick, composed of 

 brown chert (silex carne) in irregular nodules, but princi- 

 pally flattened. These are the nodules that are enveloped 

 and even penetrated by the Parisian magnesite of an Isabella 

 roseate grey colour (m). It is sometimes very pure, does 

 not effervesce with acids, and is absolutely infusible in the 

 heat of a porcelain furnace. It is sometimes slightly trans- 

 lucent. 



7. These cherts (silex) are placed on a bed F of hard 

 calcareous marl in nearly round nodules, and containing cy- 

 clostoma raumia. 



