Page:Popular Science Monthly Volume 30.djvu/204

190 the bottom along certain lines, and the Antarctic Continent, otherwise almost unknown, makes its presence felt to the dredge by the abundant masses of crystalline rock, drifted far from it to the north.

These are not altogether new discoveries. I had inferred many years ago, from stones taken up by the hooks of fishermen on the banks of Newfoundland, that rocky material from the north is dropped on these banks by the heavy ice which drifts over them every spring, that these stones are glaciated, and that after they fall to the bottom sand is drifted over them with sufficient velocity to polish the stones and to erode the shelly coverings of Arctic animals attached to them. If, then, the Atlantic basin were upheaved into land, we should see beds of sand, gravel, and bowlders with clay flats and layers of marl and limestone. According to the Challenger reports, in the Antarctic seas south of 64°, there is blue mud with fragments of rock in depths of twelve hundred to two thousand fathoms. The stones, some of them glaciated, were granite, diorite, amphibolite, mica-schist, gneiss, and quartzite. This deposit ceases and gives place to Globigerina ooze and red clay at 46° and 47° south; but even farther north there is sometimes as much as forty-nine per cent of crystalline sand. In the Labrador current a block of syenite weighing four hundred and ninety pounds was taken up from thirteen hundred and forty fathoms, and in the Arctic current, one hundred miles from land, was a stony deposit, some stones being glaciated. Among these were smoky quartz, quartzite, limestone, dolomite, mica-schist, and serpentine; also particles of monoclinic and triclinic feldspar, hornblende, augite, magnetite, mica, and glauconite—the latter, no doubt, formed in the sea-bottom, the others drifted from Eozoic and Palæozoic formations to the north,

A remarkable fact in this connection is that the great depths of the sea are as impassable to the majority of marine animals as the land itself. According to Murray, while twelve of the Challenger's dredgings taken in depths greater than two thousand fathoms gave ninety-two species, mostly new to science, a similar number of dredgings in shallower water near the land gave no less than one thousand species. Hence arises another apparent paradox relating to the distribution of organic beings. While at first sight it might seem that the chances of wide distribution are exceptionally great for marine species, this is not so. Except in the case of those which enjoy a period of free locomotion when young, or are floating and pelagic, the deep ocean sets bounds to their migrations. On the other hand, the spores of cryptogamic plants may be carried for vast distances by the wind, and the growth of volcanic islands may effect connections which, though only temporary, may afford opportunity for land animals and plants to pass over.

With reference to the transmission of living beings across the Atlantic, we have before us the remarkable fact that from the Cambrian