“Some of your scientists estimated that the volcano Krakatoa, in the East Indies, during a couple of days in August, 1883, discharged a cubic mile of materials. The volcano has had a great many eruptions in times past, and has thrown out a great many cubic miles. The materials composing the mountain itself, have all been thrown from its crater, and the same thing has happened in the case of all the volcanoes on earth, of which there are thousands. The spaces left in the crust of the earth by this process, have amounted in the aggregate to hundreds of thousands of cubic miles. Many spaces thus formed, have been filled again by melted materials pressed up from below, by the pressure of the crust upon the melted interior. But a vast amount of empty space yet remains and will continue to be added to for millions of years to come. As the earth grows older and colder, internally, the crust will become thicker and more unyielding, so that as new subterranean spaces are formed by volcanic activity, fewer of these will be filled up again and the final aggregate of them will doubtless in time reach millions of cubic miles. The spaces comprising the “Pocket” continent of the moon, above the sea level, are estimated by us to amount to about 1,500,000 cubic miles.” “This then,” I observed, “must give you a continent in there of something like 1,500,000 cubic miles, supposing the space to be a mile high.” “Yes, but that is not the shape of the interior. The ground floor of our continent at or near the sea level is only about 800,000 square miles, and it consists of thousands of separated chambers, varying from a few rods to many miles in extent, and of every conceivable shape, some being circular or oval, some long and narrow, and straight or crooked. There are a great many of the long narrow sort, extending in some cases as much as 400 miles, widening in some places to as much as ten miles and again narrowing down to half a mile. These are nothing less than cracks in our planet. They run in many directions, often intersecting each other, and they extend far down toward the center and upward in some places eight or ten miles before the sides arch together in a mighty dome. There are water marks high up the sides of these great chambers showing the sea level to have been much higher in ancient times than at present, and the action of the water on the sides has greatly widened the spaces, the materials being washed into the bottomless fissures, that extend toward the center of the planet.” “How do you account for the changes in the sea-level?” I inquired.