HISTORY OF BARBADOS. PART III. REMARKS ON THE GEOLOGICAL STRUCTURE OF BARBADOS, AND A SKETCH OF ITS NATURAL PRODUCTIONS. HISTORY OF BARBADOS. PART III. REMARKS ON THE GEOLOGICAL STRUCTURE OF BARBADOS, AND A SKETCH OF ITS NATURAL PRODUCTIONS. CHAPTER I. GEOLOGICAL DESCRIPTION. GEOLOGY, in a circumscribed meaning, is the science which makes us acquainted with the structure, materials, relative position and arrangement of the solid crust of the globe; but in a higher sense of the word it is that science which, according to the reasoning and investigation of man, gives an account of the "successive changes that have taken place in the organic and inorganic kingdoms of nature1." It is the history of our planet. As some important event, the occurrence of which we find chronicled in the pages of the past, conveys to us the cause of the rise and fall of nations and the extinction of languages, so the forms of valleys and mountains, the configuration of coasts, speak in as legible a language, to those initiated in the book of Nature, of former convulsions and of changes which lie as distant, geologically speaking, from our present time as the historical event which was the cause that certain parts of Europe are now inhabited by Celtic, Teutonic or Gallic races. Time, however, as understood in the every-day occurrences of life, comprises in a geological view a much greater space than, bafffed by a limited knowledge and fettered by prejudices, we are able to express2. The 1 Principles of Geology, by Charles Lyell, M.A., F.R.S. Seventh edition, London, 1847, p. 1. 2 One of the greatest difficulties that geology has had to contend with, is the reproach that this science is opposed to Scripture Revelation. I cannot combat such an assertion in a more persuasive way than by quoting the words of the excellent Chalmers. After reproaching such a supposition, he says, "Let no one, therefore, be checked in his inquiries into the history of the globe by anything but the good vastness of the science of geology, which combines the higher branches of physics and the history of organic and inorganic nature, assigns to it a place near astronomy, that science which carries us to the regions of infinity and the immensity of space. Thus the sublimity of Geology extends its views and researches into regions and ages more remote than any recorded by man; and the novel and unexpected truths unfolded during the progress of the science have opened to the view myriads of ages, conveying to our mind more distinctly the omnipotence of the Almighty than had hitherto been attempted by human knowledge; and hence it has been emphatically termed the sister science of Astronomy. These few observations on so great a subject must suffice to introduce those remarks on the island of Barbados which are intended to describe its geological structure. The smaller islands of the West Indian archipelago, called the Caribbee Islands, geologically considered form two groups; the western group is volcanic, and the other to the east consists for the most part of calcareous rocks. I have already alluded to the curve which these islands form with regard to their situation; and it is a remarkable fact that the outer islands, which are exposed to the direct action of the Atlantic, are calcareous, while the inner islands are volcanic. Hence Anegada, Anguilla, St. Martin', Barbuda, Deseada, and the windward part of Guadaloupe, Mariagalante, Barbados and Tobago, are calcareous; while St. Eustatius, St. Christopher, Nevis, Montserrat, Guadaloupe, Dominica, Martinique, St. Lucia, St. Vincent and Grenada form the volcanic series. Leopold von Buch considers this group as standing in immediate connection with the primitive ranges of the Caraccas; and he is inclined to believe that, if we were better acquainted with the region to the east of the Magdalena, and with New Granada and the Caraccas, we might find an uninterrupted connection of the volcanic chain between the Caribbee Islands and the Andes. Barbados is the most eastern of the calcareous chain; the general outline and aspect of this island has already been described in the third chapter of the First Part of this History: it remains now to give, as far as the limits of this work permit me, a sketch of its geological structure, and of the mineralogical character of its rocks. rules of philosophical induction, which are essential to the right use of the intellectual strength which God has conferred upon man, to be exercised on the mighty works of nature; and least of all let him be deterred from the pursuit of truth by the vain and impious dread that he may go too far, and penetrate too deeply into those mysteries, which among their other uses have this one, namely, that they continually excite to activity the soul of man; and the more they are studied, lead to deeper delight and more awful contemplation of their glorious and beneficent Author." 1 I am not quite certain whether the island of St. Martin belongs to the calcareous group. The first aspect of Barbados leaves no doubt, even to the casual observer, that its origin is to be traced to the labours of the coral animals. It presents one of the most remarkable instances of a coral island, which, by gradual and successive elevatory movements, has been raised to a height of nearly twelve hundred feet above the sea. Mr. Darwin, in his interesting work on Coral Reefs', has divided their structure into three classes, namely into the atoll, the encircling and barrier reefs, and the fringing reefs. Instances of the latter kind are very numerous in the West Indian archipelago, and the nature of a coral island composed of dead coral, and fringed by a reef of living polypifers, is perhaps best exemplified in the island of Anegada. The surface of that island is almost flat; only here and there rises a little mound; and some depressions on the western half and south-eastern point are formed in extensive ponds, some above a mile in length, resembling lagoons. The rock consists of dead coral hardened into a compact calcareous mass, and the whole island has the appearance of having been raised above the surface by one great submarine convulsion. Barbados, on the contrary, proves by its structure that the elevatory movement was interrupted by periods of rest, and hence the step-formed terraces, which, as far as I know, have no parallel in other coral islands3. It is certainly curious, if not startling, to a person who has not devoted his attention to the structure of our earth, that a considerable portion of its surface is the result of organic secretion, and that the same process still continues in operation in the warmer regions of the globe, rarely extending beyond the tropical zone1. The observations of modern voyagers, and chiefly those of Mr. Darwin during the interesting voyage of her Majesty's ship 'Beagle' round the world, have thrown much information on the structure of coral islands; and it is now believed that the coral-forming polypi began to build on submarine ridges and rocks at a moderate depth; and that while they were yet at work, "the bases on which the reefs first became attached slowly and successively sank beneath the level of the sea, whilst the corals continued to grow upwards." The structure of Barbados offers several features difficult to reconcile with this theory, which prove that it belongs to the fringing reefs. The island appears under two very distinct features, namely,— 1 The Structure and Distribution of Coral Reefs, by Charles Darwin, M.A., F.R.S. London, 1842. 2 Remarks on Anegada, Journal of the Royal Geographical Society of London, vol. ii. p. 152. 3 Mr. Darwin informs me that something similar, though probably not in such a degree, has been observed in the Pacific. The small group of islands called the Bermudas, in latitude 32° north, form an exception. It is however considered that the waters of the Atlantic, warmed by the Gulf-stream, possess a similar temperature as the seas under the tropics. 5 Darwin's Coral Reefs, p. 98. |