immaterial; but, from his own account (p. 118), there occur in one place, five or six layers of red earth, interstratified with the ordinary calcareous rock, and including stones too heavy for the wind to have moved, without having at the same time utterly dispersed every grain of the accompanying drifted matter. Mr. Nelson attributes the origin of these several layers, with their embedded stones, to as many violent catastrophes; but further investigation in such cases has generally succeeded in explaining phenomena of this kind by ordinary and simpler means. Finally, I may remark, that these islands have a considerable resemblance in shape to Barbuda in the West Indies, and to Pemba on the eastern coast of Africa, which latter island is about two hundred feet in height, and consists of coral-rock. I believe that the Bermuda Islands, from being fringed by living reefs, ought to have been coloured red; but I have left them uncoloured, on account of their general resemblance in external form to a lagoon-island or atoll. GEOLOGICAL OBSERVATIONS ON VOLCANIC ISLANDS. CRITICAL INTRODUCTION. The preparation of the series of works published under the general title “Geology of the Voyage of the _Beagle_” occupied a great part of Darwin’s time during the ten years that followed his return to England. The second volume of the series, entitled “Geological Observations on Volcanic Islands, with Brief Notices on the Geology of Australia and the Cape of Good Hope,” made its appearance in 1844. The materials for this volume were collected in part during the outward voyage, when the _Beagle_ called at St. Jago in the Cape de Verde Islands, and St. Paul’s Rocks, and at Fernando Noronha, but mainly during the homeward cruise; then it was that the Galapagos Islands were surveyed, the Low Archipelago passed through, and Tahiti visited; after making calls at the Bay of Islands, in New Zealand, and also at Sydney, Hobart Town and King George’s Sound in Australia, the _Beagle_ sailed across the Indian Ocean to the little group of the Keeling or Cocos Islands, which Darwin has rendered famous by his observations, and thence to Mauritius; calling at the Cape of Good Hope on her way, the ship then proceeded successively to St. Helena and Ascension, and revisited the Cape de Verde Islands before finally reaching England.