which form the sea floor near the shore， and which may be brought up by the mariner"s sounding apparatus， are charted for him， so that in this way he may be helped to ascertain his position.
147.The Coast of the United States. -The coast of the UnitedStates presents a great variety of features. It has long stretches of up- lifted， depressed and fiorded， dune-bordered， rock-bound， coral- and mangrove-fringed coasts. Along part of its sea border， harbors are abundant while in other portions， harbors are almost entirely lacking.
Its recently uplifted western coast has still more recently b e e n s l i g h t l y d e p r e s s e d ， thus forming the harbors of San Francisco， Portland and Seattle. This coast and the depressed and fiorded region of Alaska are paralleled， butin no way duplicated， by the One of the finest harbors in the world.
elevated south Atlantic coast which has more recently been depressed in the Chesapeake Bay region， and by the depressed and slightly fiord coast of northern New England. On the eastern side of the United States a broad coastal plain has been formed which has no counterpart on the west.
148.Influence of Coast Conditions upon Inhabitants. -Allnatural features have a greater or less influence upon the inhabitants of the earth， but perhaps none has so directly and obviously influenced man"s activities as has the kind of coaston which he lives. Europe， with its har- borfull and Africa with its almost har- bor-less coasts are in striking contrast to each other. This difference between the inducements to travel and commerce which the two continents afford is one of the factors in producing the marked difference in progress attained by the people of the two continents. They stand to-day as types on the one hand of eco- nomic progress and on the other of stag- nation.
The Ph？nicians， the Carthaginians， the Greeks， the English and the other great nations of the world have felt the enticing allurement of a captive sea waiting in their harbors like a steed forthem to mount and ride away in quest of
MINOT"S LEDGE LIGHTHOUSE.
the world"s best. Thus they have extended their conquest and influence far beyond the homeland. From the time of Peter the Great， the efforts of Russia to gain suitable outlet to the sea show the importance placed by progressive communities upon ocean traffic. The struggle of all the great world powers to strengthen their navies， no matter what the cost， shows with what jealousy the products of their ports are guarded.
Coasts with harbors give their people the facilities and inducements for seeking the unknown， while the harborless coasts confine the aspirations of their inhabitants to the products immediately around them. A glance at the coast line and harbors of Greece shows one cause of its ancient civilization and a reason why the Greeks were "always seeking some new thing."Summary. -A glance at a map shows the great variety of coast lines. The waves and tides are constantly cutting and wearing the coast. The material thus cut away is ground fine and spread out by the currents in bars and beaches， filling up coves and straightening the coast. Thus one of the results of these erosive forces is to make the coastline more regular.
Coastlines are affected not only by wind and water erosion， but by elevation and depression. When the shore rises， or is elevated， part of the comparatively even level of the continental shelf becomes the coastline. Thus elevated coasts are usually regular. But when the shore is depressed， the irregularities caused by the surface erosion on land make bays and estuaries. Thus depressed coasts are usually irregular and offer the best harbors.
Wherever there are good harbors we find seafaring people. To make ocean traffic safe， seas are charted， coasts mapped， lighthouses built and life-saving stations maintained. Water transportation is the cheapest， so good harbors are needed by all commercial nations. Nations with seacoast and harbors are usually more progressive and more civilized than inland nations.
QUESTIONS
Of what do the borders of different coasts consist？ What do the waves do to the coast？
How are beaches and bars made？
What form do the waves and currents tend to give to the coast？
How can it be shown that coasts are subject to changes in position in respect to the surface of the sea？
What are the characteristics of an elevated coast？ What are the characteristics of a depressed coast？ How are harbors formed？
How are coasts safeguarded？
What kinds of coasts are found in the United States？
How have coast conditions influenced their inhabitants？
【中文阅读】
138.长长海岸线--当我们注视地图或航海图上长长蜿蜒的海岸线时， 它不规则的形状会给我们留下深深的印象。尽管它有时也会呈一条直线延伸很 长距离，比如比斯开湾南部海岸，但若沿其两端再作一些延展，则又会看见它 变得毫无规则。那些离大陆很近，只由一湾浅水与大陆隔开的海岛，跟海岸的 地质结构很类似，它们其实也算是大陆的一部分，只是连接它们的陆地处在水 下而已。
在一些温带海洋地区，由于气候温润适宜，沿着那里的海岸线都分布着一 个珊瑚礁带，澳大利亚东北沿岸就是很典型的例子，在那里珊瑚礁可以沿着海 岸线延伸上千英里的距离。这样的珊瑚礁层，无形中对海岸线形成了一道保护 屏障，同时也在它与海岸之间构筑了一条10到30英里宽的缓流水域，为沿岸交 通提供了很大便利。
在温暖海域的海岸边，常常生长着一种叫海榄雌①的植物，它们也能起到 保护海岸的作用。它们像灌木丛一样密集地生长在海岸边的浅水区中，枝条和 根茎都向下延伸，螃蟹和牡蛎就在这里生存，海水中的泥沙和残渣也在这里被 过滤积累。由此，一些地势较低的海滩渐渐也被侵蚀成为大海。佛罗里达州和 田纳西州南岸及其他许多地方，都有这类延伸得很长的海滩。
在南北两极的附近，海岸线上都镶着一道冰圈，而在中纬度地区，海岸 一般由岩石和泥沙构成，有时还被一层厚厚的海藻类覆盖物保护着。在这一地 带，大自然的力量除了在陆地上存在的侵蚀与沉积之外，海浪和洋流也对这里 施加着不小的影响。
139.海浪的鬼斧神工--当海浪不断冲刷没有保护层的海岸之后，会慢 慢将它们磨损啃噬。磨损的速度和形式，则取决于海浪的力量强度和海岸的类型。如果海岸存在脆弱点，则这些地方会首当其冲，很快被海浪侵蚀。而那些 坚硬的部分，则会渐渐形成挺立的海岬。有些情况下，海浪也会快速地侵蚀一 些高耸的海岸，最后形成陡峭的悬崖。
如果海岸的地质构造成分不易在海浪侵蚀下分崩离析的话，便可能形成 海蚀洞。比如我们熟悉的苏格兰沿岸岛屿上的芬戈尔大海洞，那里的地质成分 主要为火成岩，因此海浪的侵蚀作用会相对更明显一些。岸边的一些喷水的孔 洞，则是由于一些容易被侵蚀的地方，被海浪磨损成了一个水平方向的通道， 并在其末端形成了通向地表的洞口，这样水一灌进去，就会喷涌出来。这类洞 穴有时还会出现在离岸边较远一点的地方。
由于海浪的侵蚀力只能作用于一个有限的深度，因此那些由裸露岩石组成 的海岸，常常被冲刷成为梯坎形状。而在水下，陡峭的反向岩石崖岸依然经受 着海浪的冲击。如果这种类型的海岸抬升起来的话，岩石梯坎就会变成面朝大 陆的悬崖。如果海岸长时间地保持同一个高度，或者它的地质构造很容易被侵 蚀的话，它之前的陆地则很可能有一大部分被海浪啃噬掉，最终变成大海。
