H4 DOMAIN I. SIDEEOUS. 



the disadvantageous situation of the bed, which 

 renders it more difficult to be worked than if it 

 were horizontal, the product amply repays the 

 undertakers, though the galleries be of great 

 length, and some even pass under the river 

 Meuse. Slate is far more valuable than coal ; 

 and yet all mines of the latter are explored by 

 pits and galleries, sometimes of immense depth : 

 those of Charleroi, in the Netherlands, are about 

 two thousand four hundred feet in perpendicular 

 depth j those of Whitehaven, in England, about 

 five thousand, while they extend more than half 

 a league under the sea. But works conducted 

 with skill overcome the difficulties which are 

 produced by these subterraneous excavations, 

 which are repaid with great profit, and no part 

 of the mineral treasure is lost. It would there- 

 fore be of great consequence to try if the method 

 of galleries could not be adopted at Angers. 



" As to the interior structure of this great 

 mass of slate, it is divided by many veins of cal- 

 careous spar and quartz, about two feet thick, 

 by fifteen or sixteen in height ; they are parallel 

 amongst themselves, and proceed regularly from 

 west to east, in a situation which approaches 

 the vertical, as they only decline seventy de- 

 grees towards the south. These veins are met 

 at intervals by similar veins, whose directiom is 



