Page:Popular Science Monthly Volume 53.djvu/22

12 an American innovation, and for the same reasons. We have here better opportunities for studying both the newer and older topographic forms, developed over broader geographical domains, and surmounting geological formations commonly of wider extent, so that the evolution of geomorphic features from the simple to the complex form is more easily understood. The explorations of the submerged topography are also along more favorable lines than in the older world. The many repetitions of the middle geological formations in western Europe, and the favorable opportunities they afford for studying certain fossils and minerals, have also distracted from the development of geomorphy there, while in America the investigations of the physical features are now occupying the most prominent place among geologists.

.—The Lesser Antilles, or Windward Islands, have often been regarded as a chain of sunken mountains, and the Greater Antilles as having been connected with the mainland. But the dissimilarity of their features, compared with those of our northern continent, and the almost general absence of the higher types of animal life in the islands, caused many to question such connections in late geological times. However, more analytical methods have brought about different conclusions.

The doctrine of the permanency of the ocean basins in the West Indian region received its coup de grâce by the discovery of radiolarian earths upon the highest land of Barbadoes, which was elucidated in the classic treatise of Messrs. A. J. Jukes-Browne and J. B. Harrison. Radiolaria are minute organisms with beautiful silicious shells, which are now forming geological accumulations at only great oceanic depths. Similar deposits also occur in Trinidad, Cuba, Hayti, Jamaica, and probably other islands. They furnish testimony of the upheaval of the floor of the ocean from depths of two miles or more. The age of the radiolarian earths in the West Indies appears to have been about the early Miocene period, which was considerably prior to the building and completion of the West Indian continent. These deposits are most interesting, as they show, upon biological evidence, the uplifting of the bed of the ocean, and later on we shall show that an equally great terrestrial movement occurred in the opposite direction, upon the sinking of the Antillean continent in Pleistocene times.

.—Such great earth movements are slow pulsations extending over large continental