The localities of geognostic interest in this large island have been referred to in the general description of the islands, and its mineralogy alone now remains to be considered.

It has been remarked above, that the muddy silts which, impregnated with the putrescent pitch of fermenting organisms, form the great mass of the flags of the “Old Red,” are exceptionally barren in minerals of interest. The cauce of this is not far to seek :—the components of such silts are not themselves those which go to the formation of many mineral bodies ;—nor have they been subjected to the metamorphic stimulus which excites to a chemical union of ingredients and elements which lie merely in the contact of granular apposition.