Moreover, in some of these islands, rocks of volcanic origin, crystalline in their structure, and totally destitute of organic remains, are associated with others of a perfectly different character, stratified and abounding in organic remains,--various species of sea shells and of coral; and it is worthy of notice, that, in one of the instances in which the appearance is best observed, viz., at Brimstone Hill, in St Christopher's, the volcanic rock, flanked by the stratified rock, and the latter--an aggregate of shells, coral, and calcareous marl, has its strata highly inclined, tilted up as it were by the former. Other islands, or parts of islands, occur, in which there are only partial volcanic traces, and these not so much of volcanic action and disturbance on the spot, as of materials, such as ashes, thrown up by volcanoes, and those distant ones. The island Barbados is an example. Composed in great parts of a calcareous aggregate, in which organic remains abound, it has very much the character, in its peculiar features, of having been raised from the bed of the ocean (where it is certain it was formed), by some mighty force, slowly acting, and which, it is probable, is acting still. Nor is there wanting in these seas instances of islands, in which almost every variety of formation is exemplified. Barbados, in its smaller portion--the Scotland district, exhibits some interesting varieties, such as beds of chalk abounding in the remains of microscopic animalcules, strata of sandstone, some siliceous, some calcareous; the one without organic remains, containing, however, deposits of coal and bitumen; the other--the latter having included in them organic remains, and of a kind to connect them with the calcareous rock of which the larger portion of the island is formed, for instance, the spines of echini and the teeth of squali. The larger islands, Trinidad and Jamaica, Port Rico, and Cuba, yield examples, still more in point. In Trinidad I am not aware that any volcano, or crater of one, has been discovered, or any rocks evidently volcanic in their origin; but from the imperfectly crystalline rocks, destitute of organic remains and distinct stratification, to clays and marls, to mud eruptions or volcanoes as these are sometimes called, through limestones and sandstones stratified, and containing organic remains, a tolerably well-marked series may be traced. In the adjoining and smaller island Tobago some of the same series are observable, but in a broken manner, not a little interesting and instructive. There, highly crystalline rocks, destitute of organic remains, are in juxtaposition with others abounding in these remains; coral rock is even found resting on granite; and in another situation the latter rock is contiguous to mica slate, in which quartz in mass is not of rare occurrence.