In time the soft mud became pressed together into solid rock, and was lifted above the sea. Perhaps not suddenly, but so slowly that a thousand years passed before it was all dry. Then terrible days came. The rock was bent and twisted by strains and heavings as the earth moved. None of these layers as we see them to-day are level. All are tilted up toward the northeast. Hot rocks, liquid, like melted lead, burst up and filled the cracks with new kinds of stone. The old rocks were frightfully burned, and changed so much that in looking at some of the pieces we can not be quite sure whether they came from the sea or not. For this reason they are sometimes called the changed rocks. However, much of the rock to be found in this part of the city clearly came from the sea; and perhaps the whole of it, except that which has been melted, was born in the ocean.
Afterward the pile of rocks was buried deep under solid ice, that ground and crushed over it as it moved toward the south. To-day you can see where the ice tore off great pieces, and scratched and polished the low hills into their present curious shapes.
I have chosen these rocks on Second Avenue because they tell so much. They show you how to read the great picture-book of the world. How do we know all these things happened? Because we see such things going on to-day all about us. The sea, the ice, the wind, the tides, and the rain are ever at work tearing down and building up. We can see the sea making sand and mud that will one day be solid rock and dry land. Surely these things are worth studying, and you must look about for other rocks, and try to read their story.
Everywhere in New York city, and in many other Eastern cities, you will see a rock that you may be very sure came from the sea. A smooth and beautiful stone that is like a story-book telling of old beaches where the surf beat with terrible fury in great storms, where the tides kept time with the moon, and of long summer days when the sea was smooth, and gentle waves fell on the white sand glistening in the sun. This is the brown stone used in building houses. It is a real sandstone.
Upon the beach you saw the sand arranged in wavy lines and curves by the water. Each creamy wave that ran up the beach left a trace showing just how far it went. The smaller and lighter particles of sand swept along by the water were dropped just at the place where the water stopped for an instant before it turned back. As the wave retreated, you remember the larger grains of sand were to be seen sorted out along the lower edge of the beach.
Look at these blocks of sandstone. Here are the same markings. Look carefully and you will soon find a piece where the sand is arranged in horizontal layers just as the water left it. Perhaps you can count a hundred layers in a single piece of stone. Some will be thick, and full of large grains of sand. There must have been a high tide that day, or perhaps there was a bad storm. Some of them will be thin, and of about the same thickness for several inches. It must have been pleasant weather then, when the sea was smooth, and each tide brought up about as much sand one day as another.
The masons in getting out the stone from the quarry cut across the layers in every direction, so that these marks are not everywhere equally plain. Yet with a little search you can soon find a perfect picture of that old, old beach. Each piece bears the finger-marks of the sea, the tracings of the moon and tides, the very handwriting of the waves. Afterward the white sand was stained with iron rust. The water bearing the iron left it mixed with the sand, and when it became dry, and was lifted above the water, the iron bound all the sand firmly together into this beautiful red sandstone, this story-book of the sea.
