Another phase of this team-work of natural forces in feeding the land to the sea is that steady advance of the waters upon certain shores. As if science herself had joined literature and art in giving the old sea dog a bad name, these advances are called in the language of geology, "transgressions of the sea." These transgressions are caused in part by the gradual sinking of the land and in part by the rising of the waters. It is not possible always to tell which agency is at work. Often both may be. One thing about the rising of the waters themselves might be looked at as particularly alarming. The rivers, which, of course, are parts of one great water system, whose centre and prime mover is the sea, are not only constantly wearing the land down toward sea level but raising the sea level by the inpour of vast quantities of ground-up land. Even as matters stand, the amount of water in the sea bowls is so great that if all lands were at the present sea level they would be covered everywhere to a depth of two miles. Wind-borne dust from the surface of the land and from volcanic explosions also, in time, amounts to a pretty sum; and, of course, helps makes the waters of the sea rise upon the land. WEARING DOWN THE LAND AND FILLING UP THE SEA Already the sea has advanced a thousand feet or more upon the coasts of Maine, to take one instance; and the whole ragged outline of Europe is due to the same cause. Let this sort of thing go on and it is easy to see that it will only be a question of a few millions of years when New York, London, and other centres of busy life will be buried like the wicked cities of the plain. And if, to help complete this picture of desolation, we for a moment forget what we learned about the life insurance carried by the continents, we can imagine how they too will disappear. And the Last Man thus: For now I stand as one upon a rock Environed with a wilderness of sea, Who marks the waxing tide grow wave by wave Expecting ever when some envious surge, Will, in his brinish bowels, swallow him.[48] [Footnote 48: Shakespere: "Titus Andronicus."] To make the thing seem doubly sure, let us reflect with Mr. Burroughs that the world is now probably in a time of spring, following the latest of the Ice Ages. If so, the water now locked up in snow-fields and glaciers among the mountain peaks will, before this summer of the centuries is over, all melt back into the sea. This alone will be good for a rise of some thirty feet in sea level. Then, still later, we shall no doubt have another Ice Age, and the only thing that may save us from being frozen to death is the fact that we have previously been drowned! II. The Builder