ments of great mountain-heights in the more elevated regions of the globe. The extensive survey of coasts, prominent among which is our own great Coast Survey. The trigonometrical surveys carried on in many countries in Europe. The investigation of the cause of the glacial epoch, and possibly of inter-glacial epochs, or a succession of alternate warm and cold periods, each extending over long epochs of time, and their effect in bringing about the present condition of the earth's surface by changes in the level of the sea and the submergence of the land.
This very inadequate statement will show how great, wide-spread, and constant has been the work of exploration and research within the period referred to, and how truly it may be denominated a geographical age.
|THE MOLLUSKS OF THE ROCKY MOUNTAINS.|
IN the summer of 1874 it was my privilege to accompany one of the parties of the United States Geological Survey of the Territories, of which Dr. F. V. Hayden is chief. The field of operations was the mountainous region of Southern Colorado, and it afforded a good opportunity to examine the natural history of the region traversed.
The mammals of the Rocky Mountains have long been well known, particularly the large game, which, except in the distant portions of the Territory of Colorado, has been greatly depleted by the constant pursuit of hunters and trappers. The case is somewhat the same with the game-birds; while the enthusiastic labors of Henshaw, Aiken, Allen, Coues, and other ornithologists, have given us a very complete knowledge of all the birds and their habitats. The fishes and reptiles have received some attention too; and, in the lower, invertebrate forms of life, the investigations of Thomas upon the grasshoppers, Carpenter on the butterflies and moths, and Edwards, Packard, and Hagen on other insects, and the reports upon Crustacea and worms by Verrill, Smith, Leidy and others, have given us a tolerable knowledge of the extent to which those forms are to be found in that region. But the mollusks of the mountains—land-snails, pond-snails, river-snails, and fresh-water mussels—have been almost entirely neglected, except by Dr. Cooper, in the north. From Colorado only seven had been reported, which were collected by Lieutenant Carpenter. This, then, seemed to be the field most needing cultivation, and my attention was chiefly turned to it during three months of wandering over the mountain-ranges, parks, and sterile plains, that diversify the country between Middle Park and the corner of Arizona. Something was found at nearly every camp, and, when the collection was at home and counted, it was