iSificious or Sandz/ Marls arc those whose dayey part 

 contains an excess of sand: for if treated \'\ith acids, in, 

 the manner above mentioned, the residuum or clayey 

 part will be found to contain above 75 per cvvt. of sand : 

 consi^qucntlj') chaiic and sand are the predominant in- 

 gredients. The colour of this marl is brownish grey or 

 lead coloured : generally friable and flakey, but some- 

 times forms very hard lumps. It does notreadily fall to 

 pieces in water. It chips and moulders by exposure to 

 the air and moisture, but slowly. It effervesces vviih 

 acids; but the residuum, after scidtion, will Dot form a 

 brick. 



Lhncslonc Qrnvcl. This is a marl mixed with large, 

 lumps of limestone. The lime may be either calcareous 

 or argillaceous; but ni'-st commonly the former. The 

 sandy part is also commonly calcareous. 



Gl/psum is a compound of calcareous earth and vitri- 

 olic acid. It forms a distinct species of the calcareous 

 genus of fossils : of which species tliere are six families. 

 The general characters of this species arc, 



1. Hohtbilif?/ in about 500 limes its weight of \vater in 

 the temperature of 60 degrees. 



2 Pr ec'tp\tab'd\ii/ therefrom by nihld alkalies, and also 

 by cg-ustic fixed, but not by caustic volatile alkali. 



3. Ineffcrvesccncc with acids, if the gypsum be pure ; 

 but some families of this species, being contaminated 

 with mild calx, slightly effervesce. 



4. InsoJiihilWy, or nearly so, in the nitrous acid, in the 

 usual temperature of the atmosphere. 



5. A Specific Gravity reaching from 2,16 to 2,31. 



6 A degree of hardness, such as to admit of being 

 scraped by the nail. 



7. When heated nearly to redness, it calcines ; and if 

 then it be slightly spiinkled with water, it again concretes, 

 and hardens. 



8. It promotes putrcfacHon in a high (]^grce. 



