410 LOWEST RED SANDSTONE. 



gradients ; the last, loses, at times, all appearance 

 of a sandstone and passes into shale and into 

 argillaceous iron stone. They also vary accord- 

 ing to the degree of induration. The prevailing 

 colours are reds, and different tints of grey. 

 They are sometimes also of a dull white, or yel- 

 lowish, or brown, or purplish, or green, or dark 

 lead blue or mottled with two or more colours, 

 as grey and red, or red and white. In this latter 

 case, the colours are often remarkably disposed, 

 as before mentioned. 



B. Quartz sand, mixed with sand or particles of 



felspar. 



a. Gravelly. 



b. Arenaceous. 



These varieties differ in aspect according to 



the relative proportions of the ingredients. They 

 also vary in colour, that being chiefly determined 

 by the tint of the felspar. The prevailing colour 

 is red, of various tones. White, and grey, arc 

 more rare. 



C. Quartz sand with carbonat of lime : calcareous 



sandstone. 



a. Gravelly. 



b. Arenaceous. 



This variety is generally white. 



