Every year the black wet soil grows firmer. Men dig trenches through it to let the water drain away. Along the banks of the river they pile the black peaty sods in long rows. This makes a dike or dam to keep the river from spreading over the grass in floods. Now the land begins to dry very fast. Wild cranberries, "cat-o'-nine-tails," and young bushes spring up. Perhaps a road is laid out over the meadows, and then houses are built, and boys and girls come to live on the smooth plain that grew out of the sea.
If you should visit the meadows at Chelsea, in Massachusetts, you would see just such a lagoon shut in by a travelling beach. It is nearly dry now, and in summer you will see the farmers cutting the salt grass. The Great South Bay on Long Island is another place where the change is going on. If you cross the Hackensack Meadows near Jersey City, you will see the work nearly finished. This vast level plain was once all water. The Passaic and the Hackensack rivers still wind through the level fields, but the work has gone so far that the land is now nearly dry. How it happened that all this great lake came to be filled up we can not tell, but we can plainly see that it was once water and is now turning to dry land.
How do we know all this about these meadows along the coast? Some of the places look very nearly the same to-day as two hundred years ago. The Indians never said that the water once flowed here. There is no record of these things. Indeed! There are plenty of records.
In the first place, you can almost always find the beach at the outside of the meadows. Nearly all the beaches on Long Island have meadows behind them. There may not be a river near, but that makes no difference, for sometimes a beach may grow across a bay between two capes.
If we dig a hole deep down into such a meadow we may find the whole story. First we turn up the black sod full of stems and roots of the grass. Under this the soil is finer, for the roots and leaves have moulded away. What's that? The spade strikes something hard. It is flat and rough, and covered with fine black mould. Wash it well, and we find it is a shell—an oyster shell. Strange that it should be there. Dig deeper, and we find more, perhaps a great quantity of them, bedded thickly one over the other. Here's the truth of the matter. This is an old oyster bed. These oysters did not come there by chance. They must have lived there, and as they live under salt-water, it is plain that where we stand was once a part of the sea.
We may dig deeper, and find more records of the old lake. See those black stones. How smooth and round they are! You remember the smooth stones we saw rolling in the surf on the beach? We can not help thinking that these stones were once tumbled about in the surf on some old beach. This is the way the marsh tells its own story, and repeats the wonderful tale of its birth from the sea.
