Upon this shelf, and for the most part within two hundred miles of the coast, are deposited all of the materials torn from the land by the sea or brought down by rivers or glaciers, excepting the very finest, which currents may float somewhat farther out, and also excepting the rocks that icebergs carry away and drop in mid-ocean; but this is not a great amount, for most icebergs strand on the shallows off Newfoundland or in Bering Sea. Almost nothing from the shores, therefore, reaches the central depths of the open oceans, whose beds are in substantially the same condition that they were in at the beginning, except for two things—volcanic upheavals in some places, and the remains of animal life everywhere. The former exception is a very important one, since it is now known, according to Professor Shaler, that volcanoes, by their eruptions, send more dust and broken materials to the seas than the rivers and shores combined. [Illustration: THE VOLCANO KRAKATOA (SUNDA STRAIT) IN ERUPTION IN 1883.] “Although the deeper sea-floors probably lack mountains,” says Professor Shaler, “they are not without striking reliefs, which, if they could be seen, would present all the dignity which their size gives to the Himalayas or Andes: the difference is that these elevations are not true mountains, but volcanic peaks, sometimes isolated, again accumulated in long, narrow ridges, but all made up of matter poured out from the craters or through great fissures in the crust. So numerous are these heaped masses of lava and other ejections from these vents that there is hardly any considerable area of the oceans where they do not rise above the surface. There are indeed thousands of these volcanic peaks distributed from pole to pole.... Thus on the floor of the North Atlantic there is evidently a long, irregular chain of these elevations extending from the Icelandic group of islands southward to the Azores. If an explorer could view this part of the sea-bottom, he would probably find that the line of craters was as continuous as that exhibited by the volcanoes of the Andes. “Besides the volcanic peaks,” Professor Shaler continues, “the sea-bottom in certain parts of the tropics ... is beset with the singular elevations formed by coral reefs.” But of these I shall have more to say toward the end of the book, and I allude to them here only as a feature of the invisible landscape beneath the waves.