North America

l many miles seaward from the present margin of the land. The boundary of our field of study is defined with considerable accuracy by a line drawn on the bot

th the outline of the submerged border of the continent; landward from it the bottom rises with a

o a mile-a slope so gentle that were the surface of the shelf exposed to view, no eye could distinguish it from a perfect plain. The deepest sounding yet obtained in the central part of the Gulf, approximately midway between Yucatan and Florida, shows a depth of 2,119

hese are the nearest approaches of the present land to the actual border of the continent to be found on the Atlantic coast. The explanation of these

Maine. The outer border of the shelf is an irregular curving line. Opposite the coast of Massachusetts and Maine an extension of the Atlantic basin reaches within 15 or 20 miles of the present marg

ofile through a

fathom curve is there over 500 miles from the coast. This is the broadest portion of the continental shelf now known on the Atlantic border of the continent. Northward of Newfo

e submerged margin of the continent is probably broad and presents a steep escarpment to the arctic basin, but

tward to the coast of Asia, and southward through Bering Strait, so as to embrace the eastern portion of Bering Sea. The continental mass of North America is thus directly connected with the continental mass of Asia. A

from 25 to 35 fathoms deep-extends to the south of the more easterly of the Aleutian Islands, and is prolonged eastward along the south border of Alaska, where the 100-fathom curve is from 10 to 20 miles from the coast-line, and approaches still nearer the land in the neighbourhood of the islands of southeastern Alaska and British Columbia. The shelf is narrow but well defined along the coasts of

ould be less in elevation above its general surface than the crests of its bordering escarpments above the adjacent depressions. The mountain-peaks when illuminated by the sun would appear as points of light with long, tapering morning and evening shadows, and the east and west plateau-borders would be strongly drawn bands of light or shadow, according to the time of day, 6,000 or 8,000 miles in length. The Bermuda, Hawaiian, and other islands now rising above the surface of the deep sea would

h, as is well known, are fringed with broad submarine terraces built in part of their own débris. In fact, every large land mass on the earth under existing climatic

and constitute the basal portions of the continental shelf, thus suggesting that the submerged platform is due, in part at least, to shore eros

avourable conditions, more than about 100 miles seaward. Supplementing the fragmental material derived from the land, and increasing in thickness towards the seaward margin of the continental shelf-coincident with the increase in depth of the water-is a deposit of light-coloured calcareous mud or ooze, formed of the hard parts of animals and plants which live in the waters of the sea. The organisms which supply this material are in the main microscopic and live especially in the war

"shells" causes the slime on the continental shelves to be calcareous and in the condition to form limestone if cemented or subjected to sufficient pressure. In the deep sea, where the hard parts of dead organisms fall through many thousands

ir seaward slopes. The shelves are thus built outward and are largely constructional topographic forms. Their outer slopes, where best defined, represent about the "angle of repose" in water of the fine material of wh

building coral-polyps, and portions of the continental shelf in that region are covered with an irregular layer of living coral and dead coral rock. The importance of this resistant superficial l

floor of the sea. This shore ice seldom travels far, and is probably not an important factor in the building of continental shelves. Of greater interest are the bergs derived from glaciers, especially in Greenland, many of which contain hundreds of thousands and even millions of cubic feet of ice and travel hundreds of miles before melting. In some instances these bergs carry with them rock masses, mud, etc., derived from the land over which their parent glaciers flowed, and as they melt, distribute this material over the sea-floor. The greater portion of this ice-carried freight derived from Greenland is dropped on the continental s

d, to Bering Sea, and to a less extent on the south coast of Alaska, where many comparatively small bergs are set afloat by glaciers which reach tide-water. Supplementing the distribution of d

f intense glaciation great additions of ice-borne débris must have been made to the continental shelf. The banks to the east of Newfoundland and other similar shoals as far south as Nantucket are probably due in large part to the débris deposited by the glaciers which formerly entered the sea in that region

st defined on the outer portion of the submerged plateau, where for a distance of 23 miles, beginning 97 miles from Sandy Hook, it has an average width of 3 miles and a maximum depth of about 2,500 feet below the surface of the bordering submarine plain, which has 20 fathoms of water over it. This ca?on opens out in the seaward face of the plateau and forms a deep notch in the generally uniform crest-line of that escarpment. Farther "up-stream," so to speak, the channel narrows to a mile and a quarter, with some irregularities in depth, and near Sandy Hook it is not apparent, owing to the amount of débris, largely sand, swept into it by shore currents. This evidence, strengthened by the fact that the true rock-cut valley of the Hudson

and the Susquehanna, while the most remarkable instance of all is furnished by the submerged valley of the St. Lawrence, which has been traced through the Gulf of St. Lawrence and out to the brink of the submerged continental escarpment s

veal the presence of submerged river channels have not been made about the shores of the more northerly portion of

e Hudson, have been discovered by soundings, some of which are thought to be true stream-cut valleys; others, how

alifornia. One feature concerning the islands referred to which is of interest in connection with the study of the continental shelf is the presence on them of numerous terraces. These occur on a series of level, step-like areas, which sweep about the slopes of the islands, in a general way parallel to the present shore-line, and are records of an upward movement of the land. The highest well-defined terrace on San Clemente occurs at an elevation of 1,320 feet, but there are less distinct beach-lines up to 1,500 feet above the p

eeds, however, to have in mind a general idea of the wonderful abundance and variety of organic forms in the shallow waters adjacent to the continent to fully appreciate the cha

ng in the waters covering it vary from place to place between wide extremes. The waters resting on it have a mean annual surface temperature of from 70° to 80° F. at the south, and about 32° F. at the north. In places great rivers and the turbid waters from glaciers bring in sediments and form muddy deposits; at other localities the currents, as in the path of the Gulf Stream off the Carolina coast, sweep the bottom clear of all light débris; and again bare rocks of limited extent are exposed. The dept

re dependent primarily on plants for their food. By far the most abundant supply of food plants in the sea is furnished by minute alg?, which float free in its water. Below a depth of about 100 fathoms alg? are absent because of lack of light, and all the de

ure, light penetrates to the bottom except in the unfavourable and fortunately restricted areas of muddy water, and motion of the waters produced by currents and the pulsation

s not compare in wealth of animal or vegetable life with certain portions of the continental shelf on the western border of the Gulf Stream. In this connection we may also cite Humboldt, who before the marvellous revelations in referenc

bundance of animal life from the wonderfully rich plains adjacent to the Gulf coast to the snow-capped mountain top. In the sea, the tropical plains with their tangled vegetation and plentiful animal life are represented by the still more uniform plain forming the submerged continental shelf with its strange forests of flowerless plants, the seaweeds. These submarine jungles shelter hosts of animal species,

ding vegetation. The water is less transparent than air, and in the deep sea it is always night. Counteracting to some extent this diminution or absence of sunlight, many marine animals are luminous and shine with

rior limit of marine vegetation is probably more definitely defined than the superior limit of land plants on snow-capped mountains. All attached seaweeds are confined to the shallow seas, but floating kelp, like the well-known Gulf weed or sargasso, which collects in the eddies of the sea currents and forms more or less mythical floating islands, is widely dist

the great shelf surrounding North America that the reader may perhaps think the cold northern ocea

of animal life to be found in shallow tropical seas decreases as one traces the continental shelf northward, but even in the Arctic Ocean adjacent to the land invertebrate life literally swarms, although the number of species, genera, etc., is comparatively limited. Seaweeds are not absent from the Arctic Ocean, althou

continental shelf off Point Barrow, the most northern portion of the arctic shore of Alaska (latitude 71° 23'), 180 species of marine invertebrates have been colle

he Kara Sea. A detailed account is given of one unusually successful haul of the trawl when it brought up large asteroids, sponges, crinoids, holothuria, a gigantic spider, masses of worms, crustacea, etc. This was the most abundant yield of the trawl-net at any one time during the voyage of the Vega on the north coast of Asia, and that, too, from the sea off the northern extremity of the continent. The temperature of the water at the surface was from zero to -1.4° C. (32° to 29.48

ea and in portions of the Arctic Ocean, the amount of life, or the tons of living animal matter per square mile in the two regions, would be in favour of the northern station is probably true. In addition to the direct evidence indicated above as to the prolific

the surface of the sea. The seals live in large numbers about all the arctic shore, and the walruses, each individual weighing about a ton, occur in herds;

POGRAPHY OF THE

ommission. The work of officers of the United States Navy in charge of Coast Survey and Fish Commission vessels, in making accurate measurements of depths, temperatures, strength and direction of currents, character of bottom, etc., has, in some instances, been commemorated on maps of the sea-floor by such names as Brownson Deep, Sigsbee Deep, Bartl

is channel when followed northward becomes shallower and broader, and opposite the Carolina coast is no longer discernible in the relief of the broad continental shelf. The Gulf Stream flows northward thr

ontour line from the land indicates a depth of 600 feet-the outer margin of the conti

mage to

ave been obtained. To the north of the Great Bahama Bank, and separated from it by water nearly 2,000 fathoms deep, is the Little Bahama Bank, measuring 50 by 150 geographical miles, from which rises the low islands known as Great Bahama, Great Abaco, and a multitude of islets and crags, while beneath the water, as is the case also on the greater submarine plateau to the south, there are numerous shoals. Southeast from the Great Bahama Bank, and in a general view to be classed with it, are several other shallow areas

ties, as on the windward border of islands, and die at other localities. The growth of coral "heads" and reefs changes the direction of currents, and the spaces of soft ooze and dead coral between the localities most favourable for coral growth are liable to be scoured out and the bottom lowered. When coral, together with the shells of molluscs and other organic refuse of the teeming life of tropical seas, reaches the surface of the water, fragments and even large masses are broken off by the force of the waves, ground into calcareous sand owing to the movements produced by the waves and currents, and much of it heaped on the borders of the reefs so as to raise them above the fair-weather level of the sea. Much of this material, when it becomes dry, is moved by the winds and built into dunes, thus still further increasing the height of th

ne plateau known as the Rosalind Bank. Even on a small map, like that forming Fig. 3, it is readily seen that in general terms there is a series of banks and low islands extending from the Mosquito Coast to Jamaica, Santo Domingo, Porto Rico, and the Caribbees. The distance measured along the curved line connecting the several areas of shallow water is about

ain of calcareous mud, roughened by countless coral crags, is a narrow east-and-west ridge in the Caribbean Sea, known in part as the Misteriosa

between Cuba and Jamaica, has a depth of 3,428 fathoms (20,568 feet) measured from the surface of the sea. Sigsbee Deep, in the central portion of the Gulf of Mexico, is a third basin of similar nature, remarkable for the great extent of its nearly level floor, which is from 2,035 to 2,071 fathoms below sea-level. (On Fig. 3 only the general depths of these great depressions are indicated.) Coupled with the profound depth of the sea in the West Indian region are the rugged mountains of the Great Antilles and the volcanic cones of the Caribbees. Some of the elevations of the land referred to are, in feet, as follows: Porto Rico, 3,609; Jamaica, 7,360; Cuba, 8

ater affording a greater degree of support than the air, but the main reason is that beneath a few hundred feet of water there is no erosion except the exceedingly slow removal of matter in solution. Could the waters of the sea be withdrawn so as to reveal the Caribbean Mountains in all of their stupendous grandeur, t

uced by movements in the earth's crust which have not been modified by erosion. The great elevations rising from the floors of the "deeps" are upraised blocks of the earth's crust which have not been bea

are largely composed of more or less consolidated ooze, such as is now found on the sea-floor in deep water. This line of evidence shows that what in late geological time was the sea-floor has been raised between 20,000 and 30,000 feet. It is thus known that both upward and downward movements of great vertical and great horizontal extent have occurred in the Caribbean region. Whatever minor changes the topography of the now submerged sea-floor may have suffered owing to emergence, the general relief, as suggested above, seems to have resulted from movements in the earth's crust, and that these movements, in certain instances at least, produced faults-that is, breaks or fissures-along

OF THE O

waves which break on the borders of the land, demand extended and painstaking investigation. The most that we can hope to do at present in this connection is to

the surface drift and the flow of the deeper currents carry the waters about in a rudely circular path, parallel in a general way with the boundaries of the respective basins. The direction of this motion, to one situated in the central part of either basin, is from left to right, or with the movements of the hands of a watch. In the southern portion of each basin there is a westward-flowing equatorial current,

e Gulf of Mexico. The waters are piled up, as it were, in that great landlocked basin, at the same time becoming warmer, and receive additions of fresh water from rain and inflowing streams. Each of these causes tends to decrease the density of the water, while evaporation has a counterbalancing influence. The escape for th

he continental shelf until it arrives opposite the Carolina coast, and thence northeastward, thus giving it a constantly increasing distance from the land. To the north of the Bahamas it receives as a tributary the portion of the equatorial current, perhaps even greater in volume than the true Gulf Stream, which is deflected northward by the West India Islands and their associated banks. Continuing its cou

rographica

Greenland, continues southward under the name of the Labrador current, past Newfoundland and Nova Scotia to the Massachusetts coast, and is thought to exert an influence on the temperature of the sea even as far south as Cape Hatteras. While the

d otherwise experience. This tendency is augmented by the icebergs carried southward with the Labrador current. In a similar way, the northward-flowing warm current gives Florida and the Carolinas a subtropical climate

orthwest coast is thus ameliorated, the prevailing westerly winds are warm and humid, and the mean annual precipitation from western Alaska to Oregon is in the neighbourhood of 100 inches. Under the influence of a mild equitable temperature and abundant moisture, the land bordering the Pacific from southern Alaska to northern California is clothed with the most magnificent forests that the continent affords. The marked contrasts in climate, vegetation, and the conditions that influence civilization between the two sides of the North American continent, produced by the cold L

the New England coast, and even farther south. The contrasts in temperature between the waters of the Atlantic and Pacific which cover the submerged border of the continent are well shown by the distribution of the cod, the most valuable of all fishes to man, which, as is well known, belongs to the northern fauna and ranges from the north Atlantic about the arctic coast of both the Old and the New Hemispheres, to the north Pacific. On the east coast of America this circumpolar fish, of which several species are known

reaks into foam. On the Atlantic coast, each tidal wave reaches the land broadside on, as it were (Fig. 4), and at the outer capes high water occurs at practically the same time from Florida to New England, but its farther landward progression is greatly modified by the shape of the coast and the depth of water in the estuaries and other indentations. When the wave as it rushes landward enters a broad water body through a narrow entrance, as the Gulf of Mexico, for example, it spreads, and as the impulse is transmitted to larger and larger volumes of water, it decreases in height. (In a critical study the tides originating in the Gulf itself should be considered.) At Galveston, Texas, the mean range between high and low tide is less than one foot. When, however, an estuary with a broad mouth receives a tidal wave from the ocean, the impulse is more and more concentrated and the wave rises higher. At the head of the Bay of Fundy the difference between high and

f the advance of tidal waves in the Atlantic and Pacifi

uch the same as the corresponding waves do in the north Atlantic, but instead

dvance as a steep-fronted wave termed a bore, which curls over and breaks in a long line of foam as it rushes along. At the head of the Bay of Fundy the bore travels at the rate of 6 or 7 miles an hour, and has a height of from 4 to 6 feet. The great disturbance produced by the strong current and breaking waves causes the mud of the bottom to be disturbed and the waters to be charged with sediment. M

ls only at high water, for the reason in general that sand-bars are frequently formed at the mouths of tidal estuaries. One of the most marked illustrations of the influence of the rise and fall of the tide on navigation occurs at St. John, New Brunswick, where the tide flows in and out of St. John River so as to form a cascade each way, dependent on the dire

d westward, and there is a prevailing current setting to the eastward. At Herschel Island, near where the east boundary of Alaska reaches the Arctic Ocean, the mean range of the tide is but 1.8 foot. At Cape S

reat diminution of the influence of wave and currents, owing to the prevalence of ice on the sea. Shore eros

R. Wallace in his Island Life two primary divisions a

t and modern continental islands have also been recognised, their age being indicated by the degree of similarity between their faunas and the fauna of the continent with which they were formerly connected. Those of ancient origin are commonly surrounded by deep water, while those which are more modern us

re plainly recent continental islands. The larger of the West Indies and the group of small islands off the California coast are also continental islands, but show by the character of their faunas and the depth of the water about them that they have been long separated from the main mass of t

PHY OF

sity embraces all classes of coast topography from the low, sandy mangrove-fringed borders of Florida and the Gulf of Mexico, to the magnifice

tions in the coast-line may be considered as forming three groups: First, the wearing away of the land through the action of waves and currents and the deposition of the débris thus prod

solution and deposition, the influence of plants and animals, the weathering of the margin of the

performed, however, with the aid of the stones which accumulate on the beaches. These are hurled against the land by the force of the landward-rushing waters and break and abrade the rocks with which they come in contact. The friction produced by the impact of waves charged with sand, pebbles, and boulders against the land leads to its removal along a horizontal belt with a narrow vertical range. The waves of the sea, in fact, act like a horizontal saw, the edge

seaward from the foot of the cliff. Of these, the cliff is by far the more prominent as it stands up boldly to view, while the terrace is in lar

of a sea-cliff and c

cceeding waves, and is carried seaward by the bottom current or undertow. During storms especially there is usually to be seen a belt of discoloured water seaward from the white breakers which margin the land. The finer débris carried away from the shore by the undertow is sooner or later deposited, and much of it is la

e sea blows obliquely to the coast, currents are established in the water which sweep along the loose material on the beach and on the submerged portion of the terrace of which the beach is a visible part, and cause it to travel in the general direction of the prevailing on-shore winds. This action

uctive and the other constructive, by which the s

ad the history as well as admire the beauties of seacoast scenery. It is not necessary, therefore, to attempt to present a detailed account of the coasts of North America from a p

the Atlantic coast

ing between them and the mainland. These features are well illustrated on the accompanying map (Fig. 6) of a portion of the Atlantic coast where long narrow bars, sometimes forming skeleton capes, are a characteristic feature. On the middle Atlantic coast of the United States the prevailing winds blow southward and there is a general southward flow of the shore currents, which carry with them the sand on the beaches and bars. An interesting fact in this connection, pointed out by N. S. Shaler, is that although the sands are continually being moved they are not worn out. After the sand-grains

.-Mobi

trance of Mobile Bay (Fig. 7), where a spit from each side has been built by shore currents so as to greatly contract the tideway between. Similar features are presented by Sandy Hook and Coney Island, each of which has been built of sand deposited by shore currents at the seaward entrance of the lower New York Bay. Another illustration of this same general character is furnished by the curved extremity of Cape Cod (Fig. 8), which is a sand-spit of

pe Cod, Ma

ance of New York Bay. These sea-built foundations are also utilized in a large number of localities for lighthouses. The waterways shut off from the sea by off-shore bars in some instances permit of the passage of vessels from one harbour to another. In

are raised but a few feet above mean sea-level, and are liable to inundation if a high tide is accompanied by an on-shore gale. A sad illustration of this plain conclusion is furnished by the disaster that overwhelmed the city of Galveston on the night of September 8, 1900, during which some 3,000 people perished and $20,000,000 to $30,000,

-Coast

vens in which boats may take refuge. Typical portions of this rugged coast are furnished by the magnificent sea-cliffs of Mount Desert and Grand Manan islands, the bold shores of Newfoundland and Labrador, and the precipitous border of Greenland. The scenery throughout nearly all of this vast extent of wave and storm beaten rocks is in striking cont

these conditions unfavourable to the work of the sea are counterbalanced by the abrasion performed by ice-floes is unknown. The northern border of Alaska, as

as been partially submerged at a comparatively recent date. The rocks in many places descend precipitously into deep water, leaving no room for the formation of beaches, and hence the waves, to a great extent, are without tools w

y to be found in the world, but to the geographer the greatest interest of this portion of the continental border, as i

ected by streams so as to form an intricate system of rugged mountain ridges and peaks, with deep, steep-sided valleys between. The degree of this roughening depends principally on the elevation of the land, together with contrasts in the resistance of the rocks due mainly to variation in hardness, climatic conditions, etc., but in general one may say the higher the land is raised above the sea the m

The débris brought from the continents by streams is laid down in shallow water-about the shores of North America almost entirely on the su

upon it, or of an elevation, which would expose a portion of the sea-bottom, thereby increasing the area of the land. A subsidence of the land adjacent to the sea permits an extension of the waters landward; the sea will enter the valleys so as to form estuaries, bays, straits, etc., while the high land between the partially

ally level country to the previous land area. The boundary between the old and new topography in such an instance would be the u

he earth's crust where ocean and continents meet. In each class there is a wide range in det

ind a map of the coast-line of North

broad, slopes gently seaward, and its continuation under the sea forms the present continental shelf (Fig. 2). Evidently a slight up or down movement or a gentle tilting of this partially submerged plain in an east and west direction would cause a marked advance or recession of the sea. Each time

rt, occupied by the sea. This feature is most marked from the Carolinas to New York (Fig. 6), where there are several great estuaries and drowned river-valleys which extend far into the land. The best examples are Albemarle Sound and Chesapeake and Delaware Bays. The James River channel is submerged as far as Richmond, the Potomac to Washington, the Susquehanna to Harrisburg, the Delaware to Trenton, and the Hudson to Troy. These are typical illustrations of what geograp

e recent movements of the land been less about the shores of the Gulf of Mexico than in the middle Atlantic region of the United States, but the rivers at the south are in general smaller and less swift than those farther north, and hence are less able to excavate broad valleys. The Southern rivers, such as the Alabama, Mississippi, Rio Grande, etc., are sil

ease and reached a maximum about the shores of the Arctic Ocean; on the Pacific coast also th

nd recent times has swayed up and down about a hinge-line situated in the region of the Gulf of Mexico, and the movements, although not uniform, have increased

ontreal, a distance of about 800 miles from the general shore-line. Still farther north are Hudson Strait and Hudson Bay, which, although but imperfectly explored, seem to be an example not only of the drowning of a r

d increase in elevation above the present sea-level, when followed northward, all the way to the arctic region, and have in the far north an altitude of about 1,200 feet. These

ue primarily to the fact that the oscillations of the land have been such that at the north the continental shelf is entirely submerged and the sea has encroach

ile at the south (Fig. 6) the shores are low, sandy, remarkably uniform in trend, and without islands, excepting such as are built by the waves and currents. The West India Islands will, no doubt, be recalled by the reader, but their history is aga

rtion of the

lan of the Carolina region. The last well-marked movement of the land in that region has been in the directi

ove the sea-level. This apparent anomaly seems to be due to an uprising of the rocks along the north side of a break, or belt of branching fractures, which closely approximates to the coast-line and has determined the position of the continental border in that region. The facts, so far as known, appear to show that we have here what geologists term a fault, the north or landward side of which has been raised at least 5,000 feet in very modern times,

y irregular coast is fringed with a belt of mountainous islands from 50 to 100 or more miles broad. The inlets between the bold capes and the straits separating the numerous islands are deep. The rugged, forest-clothed slopes with precipitous, and in many instances nearly vertical wa

t stage of the swaying of the land. On the west, as on the east border of the continent, there are drowned river-valleys, such as the Stikine, Frazer, Columbia, and Sacramento. It is not to be understood, however, that the entire Pacific coast region has been rais

st of southe

Maine, Nova Scotia, Newfoundland and Labrador, due to the partial submergence of a rugged land, lie in the same latitudes as the equally ragged coast of Washington, British Columbia, and Alaska. This is more than a coincidence. The rocks on the two coasts are similar, being for the most part resistant crys

sidence occurs produces a bold, harbourless shore without islands. The striking contrast between the deeply indented border of the continent, with its broad fringe of islands, from Mount Fairweath

although but little known, are of comparatively recent date, but differ from the coast ranges in being more largely built of young volcanic rocks. Both the coast ranges and the mountains of Central America are much less deeply sculptured than the mountains bordering the Pacific to the north of Puget Sound, and a subsidence along this shore would produce but moderate chan

ot due to stream erosion, as in the case of the drowned valley of the Hudson or of the St. Lawrence, but to the upraising of the mountains bordering it. During a former time of greater subsidence than at present the Bay of San Francisco was larger than now, a

ay from the general trend of the continental border. We have but little detailed information concerning this region,

rate size and excellence, the histories of which have not been studied. Farther south, along the Central American coast, the shores are b

ic is narrow. An elevation of 100 fathoms would add scarcely more than 10 miles to the extent of the land. This narrowness of the continental shelf seems to be due to the recency of the uplifting of the Coast mountains, and

half of North America and flowed outward across the present position of the coast-line throughout all of the northern border of the

n the land from which the ice flowed was rugged or had previously been deeply trenched by streams, the valleys gave direction to the ice currents and the margins of the continental ice-sheets became divided into separate ice-streams, as is the case in Greenland at the present day. This localization of the ice currents served to deepen and broaden the pre-existing valleys, and especially on the bold coast of Alaska and British Colum

ssion carried the glaciated troughs below sea-level. On the Atlantic coast from Maine to Labrador, and thence northward to the Arctic Ocean, there are numerous examples of fiords, as is also the case on the Pacific coast from Mount St. Elias to Pug

dified by the grinding of ice-floes, which are driven against the land by the wind. This process, however, al

s way may be recognised, namely, those laid down by the streams themselves as they drop their loads on entering still water, or delta deposits; and those spread over the sea-floor by waves and currents after receiving the débris brought from the land. Which of these two modes of deposition will prevail depends on whether the waters of the ocean at the localities where the streams deliver their loads are essentially still or are affected by strong currents. In the former inst

ted, especially by tidal currents, and ill-defined shoals, sand-banks, etc., are produced. In three conspicuous insta

elta is being extended seaward. The river divides on its delta into many distributaries and enters the sea by several mouths. The sea near the mouths of the river is reported to

am is about 90 miles. The Yukon is a graded stream-i. e., is able to carry material in suspension, but not to deepen or fill its channel-in the lower portion of its course, and is making an important addition to the land owing to the dropping of its burden of silt as soon as the still water into which it flows is reached. The stream is thus being extended, and in order to enable it to continue its task of transportation and the delivery of its load to the sea, the extended portion of its channel is built up so as to give a slope d

stance illustrates not only the manner in which coast-lines are modified, but the behaviour of a large silt-laden stream which has reduced its valley to a low gradient, and

ssippi. After United States

d divide into two or more separate channels. In the lower portion of the river some of the new channels thus formed reach the sea and furnish independent outlets for its waters. The first of these distributaries now departs from the main channel at a distance of 200 miles from the Gulf of Mexico, and farther seaward several other divisions occur (Fig. 12). The area of the delta is about 1,230 square miles. Each distributary is engaged in building a pair of embankments, or natural levees (although this process in recent years has been modified by the construction of artificial embankments for the sake of improving navigatio

ES AND

avens for the shelter of vessels fosters the interests of navigation, including sea fisheries, invites commerce from other lands, and stimulates its inhabitants to explore and travel. A diversity of industries

s and important coal and other mineral deposits adjacent to the coast or in the interior, and are near extensive and valuable fishing grounds. The best of these harbours are at the mouths of rivers

e to commercial development, namely: the rapids in the St. Lawrence between Montreal and Lake Ontario and the fall in the Niagara, and the winter climate of Canada, which causes the rivers and estuaries to be ice-bound for a considerable part of each year. To obviate the fir

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 successio

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

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 t

d 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 t

ll as the land. The broad submerged shelf fringing the continent furnishes conditions highly favoura

throughout the central and northern portions of the continent, and stands by itself as a conspicuo

ERA

apter the following books, most of which contain m

the Blake. 2 vols. Houghton

ake Shores. In United States Geological Surv

f the American Academy of Arts and Sciences, vol. xxxi

nd Portions of Costa Rica. Bulletin of the Museum of Comparat

h the Other Islands of the West Ind

nited States. In United States Geological Surv

. In United States Geological Survey, Thirteent

1894. United States Coast and Geodetic Survey.

S AND

e 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 s