SUPERIOR SANDSTONES. 425 



found of a black colour, from the presence of 

 bitumen or charcoal : the other colours depend 

 on those of the clays which enter into their com- 

 position. 



The red variety, known by the name of the 

 red marie, and already noticed, requires however 

 to be particularly distinguished on account of its 

 peculiar geological circumstances already alluded 

 to, and because it is the frequent repository of 

 rock salt and of gypsum, as well as of sulphat of 

 strontian. 



SYNOPSIS OF THE SUPERIOR 

 SANDSTONES. 



FIRST DIVISION. 



Simple : of quartz alone. 



A. An aggregate of grains of quartz, more or 

 less condensed, and varying in hardness. 



a. Of a large grain ; gravelly. 



b. Fine; arenaceous. 



The$e varieties are almost necessarily white ; 

 but they vary in brilliancy according to the qua- 



