160 On the Differences between Types in the 



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 micros- 

 copic animalcules, strata of sandstone, some siliceous, some calcare- 

 ous; 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 squall. The larger islands, 

 Trinidad and Jamaica, Port Rico, and Cuba, yield examples, 

 still more in point. In Trinidad I am not aware that any vol- 

 cano, or crater of one, has been discovered, or any rocks evi- 

 dently 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 re- 

 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. 



On the Differences betrveen Progressive, Embryonic, and Pro- 

 phetic Types in the Succession of Organized Beings through 

 the whole Bange of Geological Times. 



It was a great improvement in our zoological investigations when 

 the differences in their relations, according to the various degrees of 

 affinity or analogy which exist between animals, were pointed out, 

 and successively better understood. In earlier times, zoologists made 



