Page:Popular Science Monthly Volume 9.djvu/66

48 in the Rocky Mountains do not tally well with D'Orbigny's notes from the Andes, since out of 156 species discovered in South America, he found only 13 between the thirty-fourth and forty-fifth parallels of latitude—which corresponds to the district of north latitude considered here—and only 10 species were found above 5,000 feet. My list of the Rocky Mountain mollusca, on the contrary, shows that 55 species out of the 138 inhabit heights exceeding 5,000 feet, and 10 species have been found above 10,000 feet. These latter, however, are all recorded from mountains south of the thirty-ninth parallel; but it is safe to say that, where there is moisture, a goodly collection of mollusks can be made in the mountains of the Territories all the way up to the timber-line. This is probably true of all parts of the world.

In a recent paper on the hypsometric distribution of mollusca in Europe, communicated to the French Academy of Sciences at Paris, at their meeting on October 11, 1875, M. P. Fischer alludes to the great regularity with which plants thrive on mountains, each at a certain height. The terrestrial mollusca, being unprovided with means of locomotion enjoyed by birds and insects, and being, moreover, dependent upon vegetable life for food, could not fail to be discovered in the same way as plants, and this supposition he confirmed by observation. Each species extends to an altitude the limits of which it does not overstep. M. Fischer has verified this in the central Pyrenees as well as in the Alps, and divided the altitudes into five zones, comprised between 1,500 feet and 7,500 feet. Each zone is distinguished by the name of a species of Helix. Thus, in the Pyrenees, the first zone, ending at a height of 3,000 feet, is called that of Helix carthusiana; the second, ending at 3,600 feet, Helix aspersa; the third, terminating at 4,500 feet, Helix limbata; the fourth, limited at 6,000 feet, Helix nemoralis; and the fifth, ending at 7,500 feet, Helix carascalensis. In the Alps, at the same altitudes, the names of the zones are respectively Helix carthusiana, obvoluta, Fontenelli, sylvatica, and glacialis. A few individual mollusks will, indeed, climb as high as 9,000 feet, but they all stop at the limit of perpetual snow. Various genera of fluviatile mollusks do not ascend higher than 3,000 feet, a circumstance which the author considered of some importance to geologists, since it proves that in the quaternary beds the fossiliferous strata containing those genera, such as Neritina, Paludina, etc., were deposited at small altitudes. The Lake of Goube, about three hours' walk from Cauterets, 5,364 feet above the level of the sea, is thickly peopled with trout, frogs, and mollusks.

The results of this inquiry into the geographical distribution of mollusks in the mountainous West are meagre enough, but may be of some use in future investigations. Whether this central region is a true zoölogical province considered with reference to the mollusca, and what is the origin of its fauna, are hardly to be answered yet.