VEINSTONES. 



571 



thickness, traversing diametrically the mass of the 

 rock."* 



It appears, from the conclusion, that the Pic du 

 Midi, the chief object of these observations, is en* 

 tirely composed of primitive rocks, in distinct and 

 continued beds, or properly arrects, inclined from 

 60 to 80 ; the superior beds, immediately cover- 

 ing the limestone, being gneiss and garnet-rock ; 

 above which are numerous alternating beds or 

 arrects of limestone, trap, and sometimes of gra- 

 nite. The disposition of the trap is remarkable, 

 as it often affects, between two level beds of lime- 

 stone, folds either single or multiplied, and of the 

 strangest appearance. The granite of the supe- 

 rior beds or arrects presents many features, as a 

 vein, as a bed, and as a constituent part of many 

 calcareous rocks ; but, in the latter case, it is only 

 found on the surface, as if it had been deposited 

 soon after the compaction of the calcareous mole- 

 cules. 



Veins of granite, composed of quartz, felspar, 

 and white mica, have also been observed by Bes- 

 son, in the Limosin, in a clay slate. They are on 

 a plain which has been tilled ; and he observed no 

 granitic rock in the neighbourhood. This granite 

 is in very large and irregular grains; a circum- 



* Jour, des Mines, iv. 751. 761. 



