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.

In a letter to Dr. Heddle, Capt. Marshall Hall writes—" On the next page I give you, in complement of my last letter, the analysis of a serpentine from the Saas Thal. For the specimen I am indebted to M. Henri de Saussure. It will be interesting to compare it on the spot, and study it in its relations to the accompanying rocks and minerals.

Whether the stone is fairly serpentine with so much iron is perhaps to be questioned ; I send the analysis as that of a "reputed " serpentine, and I send it to you as you have been doing serpentines, ... . as it is possible that additional data may be of use to you.

Whilst staying at Sidmouth, in 1877, I discovered the occurrence of Celestine, Sulphate of Strontian, in cavities of Red Marl lined with crystals of Calcite, occurring in masses which had fallen from the cliff on to the shore, under the summit of Peak Hill. It appears in the form of crystals, occasionally one inch in length, which occur singly or in groups, presenting a tabular, prismato-tabular, or prismatic form,—in the latter case resembling the Barytes Crystals of Alston Moor,—and are either simple, or form compound aggregations of considerable size. In colour they are blue, wine-yellow, or of an olive-yellow hue, and as regards form, brilliancy, and transparency, surpass in beauty any examples of this mineral that I have hitherto seen. A series of the choicest specimens collected by me are exhibited in the Museum of Practical Geology, Jermyn Street.