The preglacial platform of marine erosion discussed in the following pages was first discovered in the Island of Colonsay in the course of the geological survey of that island carried out in the summer of 1907, and the information then acquired is communicated with the permission of the Director of the Survey. The subsequent tracing of the shoreline in the adjoining islands was effected with the aid of a Government grant for scientific research in the gift of the Royal Society of London. For clearness and convenience of reference the subject will be treated under the following heads:—

I. Introductory remarks indicating the aims of the investigation.

II. Colonsay and Oronsay—description of the preglacial platform.

III. Islay.

IV. Mull and Iona.

V. The Treshnish Islands.

VI. Conclusion, setting forth the present state of the subject.

Since the Omosaurus of the Kimeridge Clay may still be regarded as the only well-known European representative of the Stegosauridæ, it seemed advisable, after discussing in previous papers the Ornithopodous Hypsilophodon and the Acanthopholidid Polacanthus, to examine a representative of this type. I am therefore greatly indebted to Dr. A. S. Woodward for permitting me to do so at the Natural History Museum, and also for putting at my disposal a magnificent hitherto undescribed Stegosaurian discovered by Mr. Alfred Leeds, F.G.S., in the Oxford Clay of Fletton, near Peterborough.

Amongst the large series of specimens of Meyeria recently obtained by the Sedgwick Museum, Cambridge, from the Lower Greensand of Atherfield, Isle of Wight, two new and strange forms, obviously referable to another genus, were detected by me in looking over the material. Their interest consists not only in belonging to new species but in representing the genus Thenops, of which the best known and only British species, so far described, is Th. scyllariformis, Bell, from the London Clay. There is one imperfect specimen in the British Museum from the Speeton Clay attributed (with a query) to Thenops, but no other British representative from the Cretaceous appears to have been found.

After I had forwarded the paper on “The Residual Earths of British Guiana commonly termed ‘Laterite’”, published on pp. 439–52, 488–95, and 553–62 of the GeologicalMagazine for October, November, and December, 1910, I visited the neighbourhood of Christianburgh and Akyma on the Demerara River in British Guiana and examined a small long-deserted quarry in a very fine-grained diabase intrusive in hornblende - granitite - gneiss near the latter pluce. I obtained from the lateritic earth lying on the mass of unaltered diabase a boulder of that rook in which the central parts were ideally fresh, whilst the outer parts were decomposed into laterite. I separated these parts with great care into an outer red one, apparently an ordinary ferruginous laterite, and an inner one, buff-coloured with whitish spots in it, which was in actual contact with the unaltered rock. When I obtained the boulder these crusts were quite soft, but after a few days' exposure to the air they hardened considerably.

Some years ago the British Museum acquired from Dr. William Clark a collection of the remarkable Arthrodira found by him in the Upper Devonian shales of Ohio. In this material there are several specimens which were described as new before being brought to Europe, but concerning which there has been more or less doubt among students of the Arthrodira. Hitherto, however, it has been quite impossible to dispel this doubt since the material necessary to a comparative study of the forms in question is to be found only in America. Last year I enjoyed the privilege of going over this material in the British Museum, thanks to the courtesies extended to me by Dr. Arthur Smith Woodward, F.R.S., the Keeper of Geology, and as I had just come from a study of the American forms I was in a position to resolve these doubtful cases. The results of this study are presented in the following pages.