MODE XII. SLATE. Ill 



thin, to break them in two, by their breadth, in 

 order to prevent their fracture. These operations 

 must be performed soon after the blocks are 

 drawn from the quarry ; for if the stone has time 

 to dry, it would no longer be possible to split it. 



" The engineer Vialet, who has given a me- 

 moir on this slate-mine, says he found a mean 

 of giving these slates double their natural hard- 

 ness, which was by baking them in a brick-kiln, 

 till they had assumed a red colour. In this case 

 they are not more brittle than before; but as 

 they acquire great hardness by this process, as 

 indeed any argillaceous substances will do, they 

 ought to be formed and pierced before they are 

 put into the oven. 



" It is surprising that the slate of Rimogne 

 presents no vestige of marine bodies, while the 

 neighbouring lands are full of them ; but this 

 surprise will cease, when it is observed that na- 

 ture has formed the different portions at epochs, 

 and under circumstances, widely different."* 



Nor is his account of the slate quarries of An- 

 gers less interesting, which he places among the 

 secondary, and regards as far more rare than the 

 primitive. 



" France possesses many of these large beds 



* Patrin Min, iii. ZW. 



