[ I40 ] 



it falls to pieces, more flowly, and often into fquare pieces- 

 it alfo more flowly moulders by expofure to the air and moifture, 

 if of a loofe confiftcnce; it hardens when heated, and forms 

 an imperfect brick. — Jt effervefces with fpirit of nitre or com- 

 mon fait, but frequently refufes to do fo with vinegar — when 

 dried and projcdled into fpirit of nitre in a florence flafk, with 

 the attentions abovementioned, it is found to lofe from 8 

 to lo per cwt. of its weight. The undiffolved part, well waflied,, 

 will, when duly heated, harden into a brick. 



Siliceous or Sandy Marles are thofe whofe clayey part 

 contains an excefs of fand, for, if treated with acids in the 

 manner abovementioned, the refiduum or clayey part will be 

 found to contain above 75 per cwt. of fand — confequently chalk 

 and fand are the predominant ingredients. 



The colour of this marie is brownifh grey, or lead-coloured — 

 generally friable and flakey, but fometimes forms very hard 

 lumps, — it does not readily fall to pieces in water — it chips 

 and moulders by expofure to the air and moifture, but flowly — 

 it effervefces with acids, but the refiduum after folution will 

 not form a brick. 



Limestone Gravel : This is a marie mixed with large lumps 

 of limeftone ; the marie may be either calcareous or argillaceous; 

 but moft commonly the formef j the fandy part is alfo commonly 

 calcareous. 



Gypsum 



