24 GEOLOGY OF THE LOTHIANS. 



sandstone group ; it is in general of a brick-red colour, and 

 contains a considerable proportion of calcareous matter. 

 Unlike the clay-ironstone of the coal formation, that of the 

 red sandstone series never exhibits an internal structure, and 

 is characterized completely by the circumstance of its 

 never containing, as the former frequently does, an organic 

 nucleus. 



The white sandstone of the great carboniferous group is 

 composed of minute grains of quartz, held together by a 

 ground of argillaceous or calcareous matter : mica is often 

 present, and, as in the red sandstone, frequently produces 

 a schistose arrangement. Felspar, which is very generally 

 distributed through the red sandstone in grains, is in the 

 white far more sparingly disseminated. Bituminous mat- 

 ter occurs in great abundance in the coal sandstones, and 

 frequently is so equally distributed as to cause them to 

 assume a black colour ; whereas in the other sandstones, 

 it forms only small layers, which are arranged in posi- 

 tions parallel to the planes of stratification. By containing 

 large rock fragments, this sandstone sometimes becomes 

 conglomerated ; these conglomerates are, however, seldom 

 so coarse as those associated with the red sandstones. 

 The fragments are jasper, quartz, Lydian stone, compact 

 felspar, and flinty-slate, imbedded in an aggregate of smaller 

 masses. At Liberton Brae, a conglomerate associated 

 with the coal sandstone contains fragments of red sandstone, 

 varying in size from the smallest dimensions to the bulk of 

 a man's head. 



The slates which accompany the white coal formation 

 sandstone are of two kinds, — Argillaceous Shale or Slate- 

 Clay, and Bituminous Shale; neither of these, however, 

 possess a wide range of mineralogical character. The former 

 js in general of a grey colour, while the latter is most 



