“The caves that are at present accessible to you, are small and due to the action of water. All springs, by carrying out mineral matter in solution from below the surface, are constructing caves, and much more extensive ones than might be supposed. But those formed by the action of volcanoes, your explorers have had little opportunity to study, and, but few probably have any adequate idea of the sizes of the holes left under the surface, by the ejection of materials by volcanoes.
“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.
“As the moon cooled off, a great deal of water was taken up by the rocks, while crystallizing and thus chemically united with them, a great deal more was absorbed by them mechanically, by their pores, while a still greater quantity occupies large fissures and chambers, penetrating in all directions through the planet communicating with each other and connecting the interior waters with those of the exterior continent. The action of the water has greatly contributed, not only to the enlargement of the spaces in the interior continent, but to the creation of a pulverized soil and pleasing landscapes. The chambers that are inhabited, are of course all connected with each other, but besides these, it is quite certain there are great numbers of very extensive ones in the masses of materials that bound the inhabited chambers. Artificial tunnels are constantly being cut into these walls and so new countries are often discovered and connected with the rest and opened for settlement. In addition to those chambers that come down to the sea level the aggregate of the area of which I told you is about 800,000 square miles, there are vast areas situated at higher levels in the material, that bounds the sea-level chambers. These elevated areas are at all heights from one-fourth of a mile to four or five miles above the sea-level. There are known to be many above these, but they are not habitable, on account of lightness of the air. The elevated chambers are connected with each other, and with the lower ones, by means of sloping passages at all grades. In some cases chambers are located directly on top of the thick roof of others and are reached by long and circuitous routes. In a number of cases, the walls of sea-level chambers, after closing in almost together to form an arch over them, widen out again above and thus form other chambers above, and sometimes these stories continue one above another until the surface of the hump is reached, where the openings appear sometimes as channels, and at others, as circular craters.”
“No doubt,” said I, “the craters that our astronomers see in such vast numbers on this side of the moon communicate with your interior continent.”
“Yes they do.”
“Then is it possible, that they sometimes see down to your interior habitations? They report some of these craters, as appearing to be many miles deep.”