Page:Popular Science Monthly Volume 53.djvu/611

Rh district is about four hundred and sixty feet above the sea, but it is dissected by valleys such as that followed by the railway, whose natural divide is two hundred and ninety-nine feet. It is only reasonable to suspect that here may have been a former strait or canal, but so far the terraces and gravel floors similar to those of the Tehuantepec divide have not been described, as this is a feature of only recent scientific inquiry. The interoceanic connections referred to by Dr. Maack belong to the older Tertiary period, preceding the sculpturing of the physical features of the region, which were long anterior to the water ways here described.

—The fishes, shells, sea urchins, and other organisms of the West Indian basins belong to modern types, which to a large extent seem to have migrated from the Atlantic Ocean. Their recent appearance suggests great changes in the physical history of the West Indian seas, which are only explicable on the theory of the Antillean bridge, as set forth in the May number of this journal, and extended in the present paper. For example, the West Indian region was a high continental mass with extensive plains where the sea basins now occur, draining into the Pacific Ocean across the central part of America. With the subsequent subsidence in the mid-Pleistocene epoch the Antillean basins became seas, into which the modern Atlantic forms of life gained access. The deep-sea fishes have absolutely no relationship with those living in the Pacific Ocean, thus showing that the American barrier obtained sufficient height for their exclusion; but the littoral or shallow-water fishes and shells of the Pacific Ocean, to a notable degree, are found in the West Indian waters. The term deep-sea fauna here used applies to those forms living at greater depths than from three hundred to five hundred feet, according to circumstances. Thus it would appear that there were shallow water connections with the Pacific Ocean in or since the mid-Pleistocene epoch, such as have been shown from the study of the physical features. But these water ways were either too small or of too short duration for the general admission and commingling of Pacific and Atlantic types. The modern characteristics of the deep-sea fishes of the West Indian basins suggest that the older forms of Antillean life had been expelled from the region, so as not to permit of the development of their successors, as should have occurred if the continental area, now drowned, had not been generally drained. The modern facies of the marine West Indian life thus supports the physical evidence of a great Antillean continent or connection between North and South America just prior to the introduction of modern species. There is no inconsiderable degree of satisfaction to the student in finding that the biological phenomena support the