RED PRIMARY SANDSTONE. 341 



stone, when it assumes a white siliceo- 

 argillaceous crust. The fracture is com- 

 monly splintery with a translucent edge. 



This variety appears, at times, almost to pass 

 into compact felspar. The colours are generally 

 shades of grey; leaden, pale, or greenish ; more 

 rarely, red. 



B. Of quartz, sand and clay. 



a. The clay red, and appearing to be the result 



of decomposed felspar. 



b. With grey clay, apparently produced from 



decomposed schist, and of various shades 

 of grey, often nearly black. 



This variety passes into common fine gray- 

 wacke, arid into fine argillaceous schist, (clay 

 slate,) with which many varieties of the primary 

 sandstone alternate, as before mentioned. 



THIRD DIVISION. 



Compound : of three or more ingredients, 

 A. Quartz and felspar, with mica. 



This variety is more or less distinctly laminar ; 

 the laminae being determined by the mica. It 

 passes into a flaggy or schistose sandstone. 



