Chapter I (3)

The estuaries at the mouth of the Hudson, Delaware, Susquehanna, Potomac, James, and the Alabama, together with the distributaries of the Mississippi (which is not a partially drowned river, but one that is building up and extending its channel), are the natural outlets of portions of the continent of great fruitfulness. When other, and especially climatic, conditions are considered, it will be seen that to the geographer the Atlantic sea-border from the Gulf of St. Lawrence to the Gulf of Mexico seems destined to be the next great commercial centre in the succession from Greece to Britain. An important adjunct to the present highly favourable geographical conditions pointing to a great future for civilization on the Atlantic coast is the construction of a ship-canal across the isthmus uniting North and South America. This step must soon be taken.

A glance at a map of North America must impress one with the belief that the Pacific coast with its great extent of harbourless water-front is far less favourable to the growth or ideas, institutions, and industries than the deeply indented Atlantic shore-line. From the Isthmus of Panama to the State of Washington there is, as we have seen, but one harbour of the first class, the estuary of the Sacramento, and one of the second or third class, the estuary of the Columbia. From Puget Sound northward harbours are numberless. There are two important geographical reasons, however, why the general absence of good harbours to the south of Puget Sound is not so serious as it perhaps might seem. First, the mountain ranges run north and south parallel with the coast, and the natural lines of interior travel lead to the outlets through the Coast Ranges traversed by the Sacramento and the Columbia. The second and more general reason is that, owing to the warm currents in the Pacific, the portion of the west coast most favourable for a high degree of civilization is situated farther north than the similar belt on the Atlantic border.

* * * * *

By way of a summary of this chapter, the reader is asked to bear in mind the fact that the land forming North America, as is the case with all continents, is not at rest, but is subject to movements which cause elevations and depressions of various portions of its area with reference to sea-level. These movements have been in progress since the birth of the continent, and still continue. An upward movement of the earth's crust where the land and ocean meet causes a portion of the sea-floor to emerge and an addition usually of the nature of a coastal plain to be made to the border of a continent; while a reverse movement enables the sea to advance on the land and to flood the low-grade valleys opening to the ocean.

In a generalized view of the recent history of the coast-line of North America the dominant fact is that to the north of the latitude of the north shore of the Gulf of Mexico the resultant of the later movements of the continent is downward; the amount of the depression thus caused increases in a general way with increase in latitude on both the Atlantic and Pacific coasts. This downward movement has permitted the sea to encroach on the land and to flood many pre-existing valleys. On the Atlantic coast it produced such estuaries as Chesapeake and Delaware Bays, the tide-water portions of such rivers as the Hudson and the St. Lawrence, and farther north, where the submergence was greater, permitted the sea to invade the continental basin and form Hudson Bay. To this same wide-reaching cause is due also the bold ragged coast-line of the Atlantic from New England northward. On the Pacific border the downward movement is recorded by the tide-water portions of the Sacramento, Columbia, etc., and the deep picturesque fiords of the Canadian and Alaskan coasts. The most decided influence of these changes in the geography of the continent's margin on the affairs of men resulted from the production of numerous fine harbours and the extension of estuaries far inland, thus favouring commerce and fisheries in a high degree.

As a result of the oscillations just referred to, the sea has gained important characteristics as well as the land. The broad submerged shelf fringing the continent furnishes conditions highly favourable to both plant and animal life, and affords some of the most valuable fishing-banks of the world.

The Caribbean region is a marked exception to the broader changes that have affected the coast-line throughout the central and northern portions of the continent, and stands by itself as a conspicuous illustration of more localized earth movements which produced a remarkable submarine topography.

LITERATURE

In continuation of the studies outlined in this chapter the following books, most of which contain more special references, will be found of assistance:

AGASSIZ, A. _Three Cruises of the Blake._ 2 vols. Houghton,
Mifflin & Co., Boston, 1888.

GILBERT, G. K. _The Topographic Features of Lake Shores._ In
United States Geological Survey, Fifth Annual Report, 1883-'84,
pp. 69-123.

GULLIVER, F. P. _Shoreline Topography._ In Proceedings of the
American Academy of Arts and Sciences, vol. xxxiv, 1899, pp.
151-258. Contains a valuable bibliography.

HILL, R. T. _The Geological History of the Isthmus of Panama and
Portions of Costa Rica._ Bulletin of the Museum of Comparative
Zoology at Harvard College, vol. xxviii, 1898, pp. 151-285.

HILL, R. T. _Cuba and Porto Rico with the Other Islands of the
West Indies._ The Century Co., New York, 1899.

SHALER, N. S. _Seacoast Swamps of the Eastern United States._ In
United States Geological Survey, Sixth Annual Report, 1884-'85,
pp. 353-398.

SHALER, N. S. _The Geological History of Harbors._ In United
States Geological Survey, Thirteenth Annual Report, Part II,
1891-'92, pp. 93-209.

SHALER, N. S. _Sea and Land._ Scribner, New York, 1894. _United
States Coast and Geodetic Survey._ Annual Reports, Coast Pilot,
Tide Tables, etc.

CHARTS AND MAPS

To the student of the geography of the coast and submerged border
of North America, the extensive series of charts published by
the _United States Coast and Geodetic Survey_ supply a vast
amount of accurate information. A catalogue of these charts,
with prices, etc., is issued by the Survey. Many of the charts
issued by the _United States Hydrographic Office_, and a large
number of the topographic maps published by the _United States
Geological Survey_, are of value in this same connection. An
account of these charts and maps, with instructions as to
methods of obtaining them, etc., is given in _Government Maps
for Use in Schools_, by Messrs. Davis, King, and Collie,
published by H. Holt & Co., New York, 1894.