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there is good reason to believe that many species have become extinct since the European occupation of them. When small islands are much cultivated, many of these molluscs which can only live under the shade of forests, are soon extirpated. In St. Croix many species have become extinct at a comparatively recent period, from the burning of forests; and as we know that in all the islands many of the species are excessively local, being often confined to single valleys or ridges, we may be sure that wherever the native forests have disappeared before the hand of man, numbers of land-shells have disappeared with them. As some of the smaller islands have been almost denuded of their wood, and in the larger ones extensive tracts have been cleared for sugar cultivation, a very considerable number of species have almost certainly been exterminated.
General Conclusions as to the Past History of the West Indian Islands.—The preceding sketch of the peculiarities of the animal life of these islands, enables us to state, that it represents the remains of an ancient fauna of decided Neotropical type, having on the whole most resemblance to that which now inhabits the Mexican sub-region. The number of peculiar genera in all classes of animals is so great in proportion to those in common with the adjacent mainland, as to lead us to conclude that, subsequent to the original separation from the Mexican area, a very large tract of land existed, calculated to support a rich and varied fauna, and, by the interaction of competing types, give rise to peculiar and specially modified organisms. We have already shown that the outline of the present islands and the depths of the surrounding seas, give indications of the position and extent of this ancient land; which not improbably occupied the space enclosed by uniting Western Cuba with Yucatan, and Jamaica with the Mosquito Coast. This land must have stretched eastward to include Anguilla, and probably northward to include the whole of the Bahamas. At one time it perhaps extended southward so as to unite Hayti with northern Venezuela, while Panama and Costa Rica were sunk beneath the Pacific. At this time the Lesser Antilles had no existence.
The only large island of whose geology we have any detailed account, is Jamaica; and taking this as a type of what will probably be found in Cuba and Hayti, we must place the continental period as having occurred after the close of the Miocene, or during some part of the Pliocene epoch, since a large portion of the surface of the former island consists of beds of marine limestone from 2,000 to 3,000 thick, believed to be of Pliocene age. After some time, the land between Hayti and South America subsided, and still later that between Central America and Cuba with Jamaica; but a large tract of land remained insulated, and no doubt supported a very much richer and more varied fauna than now. We have evidence of this in extinct Mammalia of large size, belonging to the peculiar South American family of the chinchillas, which have been found in caves in the small islands of Anguilla, and which, from the character of 'the land-shells associated with them, are believed to be of Pliocene or Post-pliocene age. This discovery is most interesting, and gives promise of very valuable results from the exploration of the numerous caverns that undoubtedly exist in the abundant limestone strata of the larger islands. This extensive Antillean land, after long continuing undivided, was at length broken up by subsidence into several islands; but as this alone would not account for the almost complete annihilation of the mammalian fauna, it seems probable that the subsidence was continued much farther, so as greatly to reduce the size and increase the number of the islands. This is indicated, by the extensive alluvial plains in Cuba and Hayti, and to a less extent in Jamaica; and by elevated beds of Post-pliocene marls in the latter island.
The series of changes now suggested, will account for all the main features of the Antillean fauna in its relations to that of the American continent There remains the affinity with Madagascar, indicated by Solenodon, and a few cases of African and Asiatic affinity in insects and land-shells; but these are far too scanty to call for any attempt at special explanation. Such cases of remote affinity and discontinuous distribution, occur in all the regions, and in almost every group of animals; and we look upon them almost all, as cases of survival, under favourable conditions, of once wide-spread groups. If no wild species of the genus Equus were now to be found, except in South Africa (where they are still most abundant), and in South Temperate America, where their fossil remains show us they did exist not very long ago, what a strong fact it would have appeared for the advocates of continental extensions! Yet it would have been due to no former union of the great southern continents, but to the former extensive range of the family or the genus to which the two isolated remnants belonged. And if such an explanation will apply to the higher vertebrata, it is still more likely to be applicable to similar cases occurring among insects or mollusca, the genera of which we have every reason to believe to be usually much older than those of vertebrates. It is in these classes that examples of widely scattered allied species most frequently occur; and the facility with which they are diffused under favourable conditions, renders any other explanation than that here given altogether superfluous.
The Solenodon is a member of an order of Mammalia of low type (Insectivora) once very extensive and wide-spread, but which has begun to die out, and which has left a number of curious and isolated forms thinly scattered over three-fourths of the globe. The occurrence, therefore, of an isolated remnant of this order in the Antilles is not in itself remarkable; and the fact that the remainder of the family to which the Antillean species belong has found a refuge in Madagascar, where it has developed into several distinct types, does not afford the least shred of argument on which to found a supposed independent land connection between these two sets of islands.
Summary of the Past History of the Neotropical Region.
We have already discussed this subject, both in our account of extinct animals, and in various parts of the present chapter. It is therefore only necessary here, briefly to review and summarise the conclusions we have arrived at.
The whole character of Neotropical zoology, whether as regards its deficiencies or its specialities, points to a long continuance of isolation from the rest of the world, with a few very distant periods of union with the northern continent. The latest important separation took place by the submergence of parts of Nicaragua and Honduras, and this separation probably continued throughout much of the Miocene and Plioceue periods; but some time previous to the coming on of the glacial epoch, the union between the two continents took place which has continued to our day. Earlier submergences of the isthmus of Panama probably occurred, isolating Costa Rica and Veragua, which then may have had a greater extension, and have thus been able to develope their rich and peculiar fauna.
The isthmus of Tehuantepec, at the south of Mexico, may, probably, also have been submerged; thus isolating Guatemala and Yucatan, and leading to the specialization of some of the peculiar forms that now characterise those countries and Mexico.
The "West Indian Islands have been long isolated and have varied much in extent. Originally, they probably formed part of Central America, and may have been united with Yucatan and Honduras in one extensive tropical land. But their separation from the continent took place at a remote period, and they have since been broken up into numerous islands, which have probably undergone much submergence in recent times. This has led to that poverty of the higher forms of life, combined with the remarkable speciality, which now characterises them; while their fauna still preserves a sufficient resemblance to that of Central America to indicate its origin.
The great continent of South America, as far as we can judge from the remarkable characteristics of its fauna and the vast depths of the oceans east and west of it, has not during Tertiary, and probably not even during Secondary times, been united with any other continent, except through the intervention of North America. During some part of the Secondary epoch it probably received the ancestral forms of its Edentates and Rodents, at a time when these were among the highest types of Mammalia on the globe. It appears to have remained long isolated, and to have already greatly developed these groups of animals, before it received, in early Tertiary times, the ancestors of its marmosets and monkeys, and, perhaps also, some of its peculiar forms of Carnivore. Later, it received its Camelidse, peccaries, mastodons, and large Carnivore; and later still, just before the Glacial epoch, its deer, tapir, opossums, antelopes, and horses, the two latter having since become extinct. All this time its surface was undergoing important physical changes. What its earlier condition was we cannot conjecture, but there are clear indications that it has been broken up into at least three large masses, and probably a number of smaller ones; and these have no doubt undergone successive elevations and subsidences, so as at one time to reduce their area and separate them still more widely from each other, and at another period to unite them into continental masses. The richness and varied development of the old fauna of South America, as still existing, proves, however, that the country has always maintained an extensive area; and there is reason to believe that the last great change has been a long continued and steady increase of its surface, resulting in the formation of the vast alluvial plains of the Amazon, Orinoko, and La Plata, and thus greatly favouring the production of that wealth of specific forms, which distinguishes South America above all other parts of our globe.
The southern temperate portion of the continent, has probably had a considerable southward extension in late Tertiary times; and this, as well as the comparatively recent elevation of the Andes, has given rise to some degree of intermixture of two distinct faunas, with that proper to South Temperate America itself. The most important of these, is the considerable Australian element that appears in the insects, and even in the reptiles and fresh-water fishes, of South Temperate America. These may be traced to several causes. Icebergs and icefloes, and even solid fields of ice, may, during the Glacial epoch, have afforded many opportunities for the passage of the more cold-enduring groups; while the greater extension of southern lands and islands during the warm periods—which there is reason to believe prevailed in the southern as well as in the northern regions in Miocene times—would afford facilities for the passage of the reptiles and insects of more temperate zones. That no actual land-connection occurred, is proved by the total absence