200 



felspar from being confounded with granite, ex- 

 cept, perhaps, at the points of junction with that 

 rock. From certain varieties of micaceous 

 schist, it can only be distinguished by the predo- 

 minance of the quartz ; the limits of the two, as 

 already remarked, being evanescent. If, when 

 loose in texture, it is in danger of being con- 

 founded with secondary sandstone, recourse must 

 be had to the geological connections. 



PRIMARY (RED) SANDSTONE. 



All the varieties of this rock are not red, al- 

 though that is a prevailing character. It is most 

 generally a granular aggregate of quartz, or of 

 quartz and red clay, or of quartz and felspar : it 

 may also contain fragments of quartz, or of cer- 

 tain rocks. Its chief distinction from the red 

 sandstone of the secondary class, consists in its 

 superior compactness, and in the prevailing in- 

 termixture of a continuous crystalline with there- 

 united, or arenaceous, structure. It will, how- 

 ever, always be necessary for the student to have 

 recourse to the geological position. It cannot be 

 confounded with granite, if as in the case of 



