182 RED PRIMARY SANDSTONE. 



in the fineness of the ingredients, exceedingly indu- 

 rated, and the grains bearing the marks of previous 

 mechanical attrition. In this respect, indeed, it often 

 equals common quartz ; the whole appearing as if 

 cemented by a general solution of silica. 



Sky presents the most easily ascertained examples of 

 this rock: though it occurs also in Ross and Sutherland, 

 associated with quartz rock. The beds, which follow 

 the general direction, present almost every possible 

 dip, being directed also to different sides of the ver- 

 tical. If their present lateral breadth be considered 

 the same as their original depth when they were depo- 

 sited, they will be esteemed to occupy a thickness of 

 many miles. But, I have pointed out how such an 

 estimate may be fallacious ; though, under any view, 

 they will form a mass of enormous thickness. In Sky, 

 this series of beds is also in parallel contact with the 

 gneiss with which it alternates ; but, as in most cases 

 of erected strata, it is impossible to decide which was 

 originally the lowest. Independently of this alter- 

 nation, by which its primary nature is established, it 

 also graduates into the gneiss, producing intermediate 

 substances noticed under the head of that rock, and 

 consisting in different modifications of chlorite and 

 argillaceous schists, from fine slate to a perfect con- 

 glomerate, occasionally also containing garnets. These 

 alternations are sometimes very frequent, and the beds 

 of schist are minute in proportion to the sandstone ; 

 in other cases, considerable accumulations of the 

 schistose beds, unmixed with sandstone, occur. Con- 

 glomerates of various structures alternate with the 

 finer sandstone, as in the case of the secondary strata. 

 Lastly, quartz rock is found in the same places, alter- 

 nating with this sandstone, and forming an integrant 

 member of the series ; with the same variety of charac- 

 ter as where it occurs with micaceous schist. 



