Sometimes the materials of a coastal plain are found far inland in places which are now separated from the sea by mountain ranges, as near Lake Ontario. But the method of formation was the same, only thousands upon thousands of years have passed since these rocks were exposed, and vast geological changes have taken place in that time. Such areas as these are sometimes called ancient coastal plains.
In the western part of the
United States the coastal plain is not as well developed as on the Atlantic border. But the region about Los Angeles is a coastal plain, and almost all the characteristics of the broad eastern plain can be seen in traveling from the ocean to theCRUDE TURPENTINE STILL.
In the pine belt of the North Carolina coastal plain.
coast mountains.
182.Industries on Coastal Plains. -The valuable minerals of the earth are usually found in the older rocks, so there is no mining on a coastal plain, and because the rivers are shallow and fall over no ledges as they flow across these plains, no great water power for manufactur- ing can be developed. The sluggish streams are often dammed and small water powers developed, but there is not the fall necessary for large factories, except sometimes in the hilly region back near the old land where the rivers have developed rather deep and narrow valleys, and mill ponds of considerable size may be made.
As the different kinds of soil lie in belts, agriculture will vary with the belts. In warm climates rice can be raised along the shore where the land is marshy. On the sandy land most profitable truck farming is possible if the transportation facilities are good. In many places in the southern states these sandy areas support fine forests of pine which are most valuable for the production of turpentine, tar and lumber. Where thesoil is not too sandy, cotton is raised in abundance. The materials for makingCOTTON.
A most valuable product of the southern coastal plain.
glass, pottery and brick are widespread over coastal plains.
The cities on coastal plains are usually found either (1) near the coast, where the rivers have formed harbors and so have made ocean commerce possible, or (2) at the head of navigation in the rivers where water transportation begins, or (3) still farther up the river at the fall line, where manufacturing on a large scale is possible.
The fall line is the point on a river where its bed passes from theharder rock of the old land to the softer material of the coastal plain. The softer material is worn away more easily than the hard material, and falls or rapids are produced suitable for water power. A glance at a map of the southeastern United States will show that the principalPINEAPPLES.
A valuable crop of the southern coastal plain.
cities lie in lines nearly parallel to the coast. Of those near the coast are Norfolk, Wilmington, Charleston, Savannah, Jacksonville; at the fall line, Trenton, Philadelphia, Richmond, Columbia and Augusta.
Coastal plains furnish a most suitable place for the boring of artesian wells. As the strata are diversified in structure and all dip gently toward the sea, porous strata inclosed above and below by impervious strata are readily found. When the upper of these are tapped, water is forced by hydraulic pressure to a height nearly equal to the highest point reached by the upper stratum. Much of the drinking water on coastal plains is obtained in this way.
183.Embayed Plains. -If a coastal plain is submerged after it hasbeen somewhat eroded, the water backs up into the stream valleys and forms re?ntrant bays. The little side streams which enter into the main streams near the coast no longer flow into these streams but into the bays. If the country is somewhat thoroughly dissected near the coast, there will be many small bays. The interstream areas will project out like long fingers with water between them.
A SUBMERGED COASTAL PLAIN.
The effect of a submerged and eroded coastal plain is seen in the Delaware and Chesapeake bay region. Here the old river courses have been submerged, and the land between the rivers extends into the ocean in narrow, rather flat strips with many little inlets along the sides. Easy water communication is here possible to a considerable distance inland and to almost every part of the land surface near the coast.
When the country was first settled, these water courses were most advantageous to the settlers, as the produce of the farms could be transported to sea-going ships with comparatively little difficulty, much more easily than would have been the case if it had been necessary to carry it by land. There was little need of building roads, as each farmer had a protected water highway to his door. Thus a part of this region was known as "Tide-water Virginia."184.Lake Plains. -Lakes which receive the drainage from the land gradually have their floors smoothed over by the sediment which the streams bring to them and the waves and currents spread out. The lake itself is thus filled, or in time the outlet wears back so as to drain the lake. Thus a plain is left, the elevation of which is determined by the elevation of the old lake bed.
During the Glacial Period lakes were held in at some places by huge dams of ice and at other places by accumulations of sand or gravel brought down by the glaciers and deposited so as to obstruct the valleys. The ice has now disappeared and the gravelly material has often been easily eroded, so that lake plains are not uncommon in the northern United States. As the soil of these plains is fine and easily cultivated, they furnish excellent farm lands.
