WHAT HAPPENED WHEN THE EARTH SLOWED UP
But there is another thing that may have helped to make many great mountains run north and south. Bedtime and sunrise used to come a good deal oftener than they do now, for then the earth turned faster on its axis. It turned fastest of all at the equator, just as it does to-day. So the lands in the equatorial belt were pulled up and the belt enlarged. Then, as the speed of the globe slackened, the enlarged belt began to wrinkle because there was not the same amount of centrifugal or "fly-away-from-the-centre" force to make it stand out. So wrinkles came at right angles to the belt, just as do the waist gathers in a dress.
And now about the mystery of the mountains and the sea. When we visit the rock mills of the sea along in October[20] we shall notice, among other things, that the rock is made along the sea border, and that the coarsest sediment settles nearest the land. As a result this part of the deposit is built up faster than that farther off shore, and as it gets heavier and heavier it sinks. The deposits farther away from the shore sink, also, but more slowly because these deposits are not piled up so fast. Now, if you come down on one end of a seesaw what happens to the other end? It goes up, doesn't it? The effect of this sinking of the rocks of the sea upon the rocks of the adjoining land is something like that. The rocks that make the continents extend out under the sea, and the weight of the newly laid stone on the sea margin end not only tips the rock beds up, but, sinking in toward the continental mass, wrinkles it up, as the pages of this book will wrinkle if you push them from the front edge. So you get your mountains along the sea border. And they are in parallel ranges, because the land is crumpled up into several folds, like a table-cloth pushed from one side.
[20] [Chagter X], "The Autumn Winds and the Rock Mills of the Sea."
"But," you say, "how about the Rocky Mountains? And the Carpathian Mountains in Europe, not to mention several others? They are not on the borders of the sea."
WHY SOME MOUNTAINS ARE FAR FROM THE SEA
That's no sign they weren't near a sea border at some time. Let me just ask you. Suppose you found that most of the great mountain chains are on the borders of seas, and suppose you had figured out the reasons I have just been giving, then what would you do if you found a few mountains far back from the sea? You would probably try to find how they got moved back, wouldn't you? That's just what other men of science did. A study of the rocks of the mountains themselves and other things bearing on the question goes to show that since the mountains were made the sea might have retired from regions where it had previously advanced, as it did in the case of the Mississippi Valley, or the land may have risen between these mountains and the sea. Moreover, the down wash from the mountains themselves sometimes builds wide lands, which, as they extend and shut back the sea, leave the mountains farther and farther away. Much of the land extending east from the base of the Rocky Mountains was made in this way. The Mississippi Valley was for ages, you know ([page 10]) the Mediterranean Sea of North America, lying in the downward fold of our continent between the Rocky Mountains and the Appalachians.
From the painting by David James
THE WAVE