494 DOMAIN V. CALCAREOUS. 



flat, of two feet diameter, and seven inches 

 thick; all the exterior crust is calcareous, gra- 

 nular, greyish, and a little argillaceous : it is an 

 inch and a half thick. The interior of this Indus 

 is filled with gypsous prisms, greyish, penta- 

 gonal and hexagonal, with interstices between 

 them. These prisms are two or three inches in 

 height, and one in diameter; their surface is 

 strewed with small brilliant crystals. 



" The farinaceous gypsum, or white gypsous 

 earth, is sometimes found in the form ofguhr^ 

 but the crystalline gypsum forms considerable 

 beds : they are often intermixed with grignards* 

 or crystals of selenite, forming continued layers. 

 Lenticular selenite is found in the marl : these 

 crystals, grouped in different ways, have been 

 precipitated from the aqueous fluid which held 

 them in solution; the marl, which has after* 

 wards settled, has encrusted, surrounded, and 

 protected them. They are found in great quan- 

 tities at the foot of Montmartre, towards Mou- 

 ceaux. 



" Basaltic selenite, or in hexahedral prisms, 

 with trihedral summits, alternate, with a curved 

 surface, is found in the marl, near the summit 

 of the hill of Belleville. 



" Prismatic decahedral selenite, produced by 

 the elongated octahedron, truncated near its 



