CLAY, MARLE, AND SAND. 609 



arises a geological interest not here admitting of dis- 

 cussion. 



It is unnecessary to enumerate more varieties 

 of a substance of which the composition and 

 characters are so unsteady. The clays pass into 

 shale, sand, and marie, and contain ironstone, 

 pyrites, gypsum, and various organic remains. 

 Menilite is found near Paris, in some cases, in a 

 clay marie. Lithomarge, bole, tripoli, and other 

 partial substances, cannot claim places in this 

 enumeration. 



MARLE. 



A. Simple, or earthy. 



a. Massive, more or less compact. 



b. Schistose, marie-slate. 



Some of the specimens of both these, fall 

 into pieces by exposure to air, and then be- 

 come plastic. They occur, principally, with the 

 secondary limestones, and vary much in their 

 appearance, colours, and composition. They 

 pass into shale by the diminution or loss of the 

 calcareous ingredient. 



R R 



