THE NORTH ATLANTIC COAST PLAIN 213. How this land was made.—Once upon a time, a very long while ago as men count time, but a very short while ago when time is reckoned by the age of the world, what is now the eastern coast of North America was down under the sea. Then very, very slowly it was lifted up, so that what had been sea bottom became dry land, flat and level, made of clay, sand, and mud that had been washed down by the eastern rivers of North America. One can dig a deep well in the plain and not reach solid rock. The plain thus made extends from Cape Cod all the way around to Mexico. There are many such coastal plains in the world. That part of our coastal plain north of the Cotton Belt we call the North Atlantic Coast Plain.
214. The beach and the fall line.—At the eastern edge of this region is the sea, with its waves ever beating upon the sandy beach. At the western edge of the coast plain lies the hilly Piedmont region. What is now the surface of the Piedmont was once deep down under the earth where the great pressure of the overlying rock helped to turn sand and clay into hard stone. But it has been above the sea level for ages and ages, and the streams and weather action have worn it down till it is not much higher than the surface of the Coastal Plain.
Look on the map (Figs. 21, 241) and see how the streams and rivers, as they flow down toward the sea, cross first the hard, rocky Piedmont earth, soft, sandy earth of the Coast Plain. In the rocky region the stream wears away its bed very slowly, but in the earth of the plain it quickly digs a much deeper channel. Because the streams wore away the sandy soil so much more easily than they did the hard rock, a wide ledge of rock is left in every stream along the eastern edge of the Piedmont. Each stream that enters the Coast Plain from the Piedmont region tumbles over the last rocky ledge in falls or swirling rapids. This chain of rapids is called the "Fall Line". It extends from New Jersey to a point at least as far as Augusta, Georgia.
Boats going up the rivers have to stop when they come to the ledge of rock where the rapids are. This fall line is a natural place for men to make towns. Why? Throughout its length it is now marked by a row of cities, sometimes called fall-line cities: Trenton, on the Delaware; Philadel phia, on the Schuylkill; Baltimore, on a creek called Jones' Falls; Washington, on the Potomac; Richmond, on the James; and Raleigh, on the Neuse River. These cities, except Baltimore, we shall study in connec tion with the Northern Piedmont Region. (Sec. 264.) The Coast Plain includes Long Island and Cape Cod, both of which are as sandy as any other part of the plain.
215. A climate boundary.—The southern boundary of the North Atlantic Coast Plain is a climate boundary, and it is found at the place where the growing season is long enough to let cotton ripen and become an important crop.
216. Waterways and harbors.—After the North Atlantic Coast Plain had been raised out of the sea, and the rivers had cut valleys in it, a part sank fifty or sixty feet, and, of course, the sea flowed back into the river valleys. Look at the map, and you can see that the ocean water filled up the Susque hanna River valley and made Chesapeake Bay, and you can see that it filled the lower parts of many branch valleys that now make the arms of the big bay. On another part of the coast the water joined two little valleys which have become Long Island Sound. Look at the map (Fig. 26) and tell how two valleys filled with water made the State of Delaware a part of a peninsula. How can boats pass from the Chesapeake to the Delaware? Many steamboat lines go from Baltimore to Norfolk, Fredericksburg, and to York town, and to many, many other places on both sides of Chesapeake Bay. These boat lines have greatly helped to make Baltimore the large, prosperous city that it is. Many counties in the CoastPlainsection of Virginia have, even now, no railroads, but depend upon sailboats, launches, and steamboats.