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108. The Northern Ocean is enclosed between the northern extremities of the two continents. It is connected with the Pacific Ocean by Beering's Straits, about 48 miles in width; and with the Atlantic, by the sea or passage which separates Norway from Greenland. This ocean has usually been considered as extending about 3000 miles, from Beering's Straits to the Atlantic, and is supposed to be chiefly covered with ice. But even the coasts of Asia have been but partially explored, and we know little of the quantity of land it contains. The extent of Greenland is unknown; and the recent discoveries of the British expedition, under the command of Captain Parry, render it probable that there is a considerable tract of land east of this, which is not connected with North America.

109. The Southern Ocean lies round the south pole, extending to Cape Horn and the Cape of Good Hope. It forms an immense circular zone of water, embracing only a few bleak and desolate islands.

110. The Pacific Ocean lies on the west of America. It extends from Beering's Straits, about 8000 miles to the limits of the Southern Ocean; and from America to Asia, about 11,000 miles, or nearly half round the globe. It contains numerous clusters of islands, lying chiefly between the tropics.

111. The Indian Ocean is a branch of the Southern, extending into the Eastern Continent between Africa and New Holland. Its extent from east to west is from 3000 to 6000 miles; and from north to south, about 4000 miles. Between this ocean and the Pacific, are the Asiatic islands, and those which compose Australia. The whole of these are sometimes considered as belonging to one sea, termed the Indian Archipelago.

112. The Atlantic Ocean, lying on the east of America, is from 3000 to 4000 miles in breadth, between America and Europe; and 9000 in length from the Northern to the Southern Ocean. Between Norway and Greenland, the breadth is not more than 700 miles; between the capes of Africa and South America, it is about 1500.

113. When a considerable branch of the ocean is almost surrounded by land, it is called a sea.

114. A narrow passage of water into a sea, or between two portions of land, is called a strait.

115. A wider passage is called a channel. A sound is a channel which may be sounded.

116. When a part of the ocean runs up into the land, with a broad opening, it is called a gulf or bay.

117. A harbour is a small bay, where ships may anchor. A road is a place of anchorage on an open coast.

It will be useful to consider each of the oceans separately, and examine the branches and subdivisions which extend into the land around it. Thus it will be seen on examining the maps of the World, Europe, and Africa, that the Atlantic Ocean extends into the Eastern Continent, forming the Gulf of Guinea, the Bay of Biscay and the Mediterranean, Irish, North, and Baltic Seas. These seas are connected with the ocean by straits and channels; and each spreads into other smaller branches, forming gulfs, bays, and harbours. The following questions with the aid of the maps, will show their connections, and give more distinct and permanent ideas than a description.

Questions. Describe the situation of each of the great branches of the Atlantic on the Eastern Continent. (See the maps.) Mention the passages leading to each. What branches has the Baltic Sea? The North Sea? The

Irish Sea? What are the branches of the Mediterranean on the northern coast? What is the principal one on the southern coast? (The eastern part of the Mediterranean is often called the Levant.)

Describe the principal branches of the Atlantic in the northern part of North America. (See map of North America.) What are the two branches between North and South America? What are the passages leading to each? Mention the chief branches of Baffin's Bay. Of Hudson's Bay. Of the Gulf of Mexico. Of the Carribbean Sea.

What are the principal branches of the Atlantic, on the eastern coast of the United States? What are its principal branches on the coast of South America? (See map of South America.)

What straits connect the Atlantic Ocean with the Pacific? What branches of the Pacific are there on the western coast of South America? What bays, sounds and gulfs on the western coast of North America?

What great branches of the Pacific on the eastern coast of Asia? (See map of Asia.)

What gulfs in the Chinese Sea? What passages connect the Pacific and Indian Oceans? What gulf penetrates the northern coast of New Holland? What are the two great branches of the Indian Ocean, extending into Asia? What on the coast of Africa? What of the Arabian Sea?

SURFACE OF THE LAND.

118. The surface of the land may be considered under the two general divisions of highlands and lowlands.

The highlands are the highest parts of the earth, sometimes rising in the abrupt peaks and chains of mountains, and sometimes forming extended plains.

The lowlands, or less elevated portions of the land, are sometimes irregularly diversified with hills and valleys. The principal divisions are plains and vales.

119. Mountains are the highest prominences on the surface of the earth. They sometimes occur single; but they are generally united in chains or ridges, of various lengths and heights.

120. Volcanoes are mountains which send forth fire and smoke from their tops.

121. Plains, whether of the highlands or lowlands, are extensive, level tracts, which are not diversified with mountains

and valleys. In Asia they are called steppes. An elevated plain is called a plateau or table-land.

122. Deserts are extensive plains, which are almost destitute of vegetation, and contain few springs or streams of water. 123. A body of water enclosed by the land is called a lake. A salt lake is sometimes called a sea, as the Caspian Sea, and Sea of Aral in Asia.

124. Rivers are large streams of water, composed of numerous smaller streams or branches, and flowing from the mountains or highlands into the sea.

125. The place from which a river runs is called its source; and the place where it empties, its mouth. When the mouth of a river is broad, it is called an estuary, or frith.

126. Vales, or river districts, are hollow tracts, bounded by hills, which are watered by a river.

127. A basin is a tract of country, embracing a large river and numerous branches, which drain off its waters, and includes a number of vales.

128. A declivity is the gradual descent from the highlands to the lowlands, or the bed of the ocean.

129. The highlands, lowlands, and declivities, form the face of a country, and often have mu. influence on its climate and fertility.

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130. Rivers usually descer by the shortest course, from the highest to the lowest parts of a country. They sometimes pass through chains of mountains; but in general, the highest parts of a country are those from which its rivers rise; the lowest, those in which they empty; and the land usually declines, in the direction from their sources to their mouths. Hence we

may learn the face of a country by tracing the course of its rivers.

131. A number of declivities usually surround every large body of water, descending in different directions from the mountains.

Thus, in looking at a map of North America, it is evident from the course of the rivers falling into the Atlantic Ocean, that the declivity of the Atlantic states is towards the south-east. It is also evident, that there are declivities in different directions around Hudson's Bay. On the map of Europe, Spain will be seen to have several declivities; Italy two principal ones; and several may be observed around the Baltic Sea.

Let the student trace on the map the declivities of Spain-of Italy-of South America, &c.

EXERCISES ON THE MAPS.

Trace the rivers of the north of Asia, and find in what direction the land declines. What other declivities in Asia? Which appears to be the highest portion of Asia? Trace the declivities of North and South America in the same manner. Describe the declivities around the Baltic and Mediterranean Seas. Describe those of France and Italy.

STRUCTURE OF THE EARTH.

132. The solid parts of the Earth consist of various substances, on whose nature the surface, soil, and waters of a country, and to some extent, even its climate, salubrity, and wealth depend.

133. The description of the structure of the earth, and the materials which compose it, is called Geology; and some acquaintance with this subject is necessary to a complete knowledge of geography.

[17] 134. The perforations of mines extend about half a mile in depth, and we are acquainted only with the external layers or crust of the earth. But the same minerals which exist on the surface, are found at the greatest depths yet examined, and are thrown out from the craters of volcanoes. It is therefore probable that the great body of the earth is composed of similar materials.

135. So far as the body of the earth has been examined, it consists of various strata, or layers of rock, one above another, differing in their nature, extent, and depth. (See the figure.) Eighty strata, of different kinds, have been found in a depth of 500 yards.

136. The direction of the strata is sometimes horizontal, sometimes inclined, and sometimes waving with the surface of the ground. When they are perpendicular, they are called tables.

The different strata of rocks resemble the different books in a pile; and a single stratum is sometimes divided into leaves or lamina; but not always in the direction of the strata.

137. The strata of rocks are frequently separated by clefts or seams. Sometimes these are open, forming chasms and caves; and sometimes filled with some other mineral.

138. When a cavity or seam which lies between the strata, is filled with another rock or mineral, as is often the case with coal, salt, &c. it is called a bed. If it runs across the strata, as is usually the fact with metallic ores, it is called a vein.

139. Near the surface of the earth, and often for some distance beneath it, we find rocks which contain the remains of land and marine animals, vegetables, and fragments of other rocks. It is hence concluded that they were formed after the existence of animals and vegetables, and they are called secondary rocks.

Sometimes whole mountains are formed of rocks chiefly composed of shells; as some among the Catskill Mountains of New-York, the Pyrenees, and many other chains. These remains are found on the loftiest portions of the globe, among the Alps and the Andes.

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(7.) Strata of the Earth.

P. Primary Strata; T. Transition; S. Secondary; A. Alluvial; B. Basaltic; V. Vein; b. bed.

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(8.) Section of the Earth between latitude 40° and 45o.

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