40 DOMAIN VIII. DIAMICTONIC. 



some portions, as usual in the infinite variety of 

 nature, the quartz will preponderate, and some- 

 times the siderite. Saussure's description is as 

 follows : 



Glazed rock. W e now arrived at this singular rock, which 

 formed the object of this excursion. Its supe- 

 rior surface inclines to the east, under an angle 

 of 43 degrees. It is this surface which is po- 

 lished, and in so bright a manner, that it forms 

 a perfect mirror. In some parts it is perfectly 

 plane, so that tables might be cut from eight to 

 ten feet in length, and of a proportional breadth ; 

 while in other parts it is a little undulated, but 

 still equally polished. It is here veined like a 

 marble; there marked with angular spots, like 

 fragments enchased in a base. The coloiir va- 

 ries, the ground being commonly brown or 

 blackish, and the spots of a pure white; some- 

 times however the ground itself is white. This 

 stone is very hard, yielding abundant sparks 

 under the flint, whence the polish resembles that 

 of an agate or a jasper, having more splendour 

 than that of marble. The white parts are un- 

 doubtedly of semi-transparent quartz, infusible 

 by the blow-pipe, but dissolving very speedily, 

 and with a lively effervescence, in mineral alkali. 

 The black parts appear of two kinds ; those 

 which are nearest the polished surface losing 



