LOWEST, OR OLD RED, SANDSTONE. 215 



for the puipose of illustrating its general features. 

 Such mountains rarely present a rugged outline, and 

 seldom display the naked rock, except in their torrents 

 and sea cliffs ; as in those of Shetland, Orkney, and 

 Caithness. Such is its general facility of decomposi- 

 tion, that the inclined surfaces soon become covered 

 with rubbish, and, finally, with vegetation ; while the 

 cliffs and ravines, from their perpendicular nature and 

 the frequently low angles of the strata, long preserve 

 their original forms, so as to produce a well-known 

 peculiarity of character. 



An exception however occurs in the case of the 

 conglomerate beds, which, from being of a harder tex- 

 ture than the finer sandstone, often remain after the 

 softer parts have mouldered away; sometimes present- 

 ing insulated masses with vertical faces, or rising into 

 the more fantastic shapes of pinnacles and towers ; as, 

 Very notedly, in Montserrat. On Kea cloch, the finer 

 sandstone also produces a serrated outline, resembling 

 that of granite, from the same cause. The softer kinds 

 are often deeply covered by alluvia, displaying the 

 gradual progress of decomposition, from the solid rock 

 ' to the loose red clay ; while the rock often disappears 

 entirely, as in Arran and Cantyre ; the depth and 

 colour of the soil alone remaining to mark its former 

 situation. ., 



The soil which covers the red sandstone is extremely 

 variable ; from the various proportions of clay, and 

 sometimes of calcareous earth, which enter into it, or 

 from the presence of argillaceous and marly beds. In 

 the central districts of Scotland, there is often an ad- 

 ventitious soil upon it, the produce of former masses 

 of Trap ; and hence is explained the diversity of as- 

 pect which these districts present, from the most fertile 

 to the most worthless. In Shetland, where this sand- 



