The eastern part of the plain, toward the base of the Alleghany Mountains and the shores of Hudson Bay, are generally wooded, and diversified by hills of trifling elevation. The middle parts, embracing the valleys of the Mississippi and Missouri, and the intervening tracts as far as the upper portions of the Mackenzie, are level and grassy regions, called prairies. 121. Prairies may be arranged into three kinds :

(1.) The Bushy Prairies.-These usually contain springs, and are covered with grass, shrubs, grapevines, and varieties of flowers.

SCENE ON AN AMERICAN PRAIRIE.

(2.) The Dry or Rolling Prairies, so called from the absence of swamps or pools, and on account of their wavy surface. The vegetation consists principally of grass, weeds, and flowers, which grow with great luxuriance. Over these prairies the American buffaloes roam, in herds of from 40,000 to 50,000.

3.) The Moist or Wet Prairies, the smallest division, abound in pools without issue, left by the floods of the rainy seasons. They are covered with a rich vegetation of tall rank grass.

122. Along the Atlantic coast, between the base of the Apalachian Mountains and the sea, stretches a plain, or a comparatively level region, narrow in its northern portion, but increasing to a width of about 250 miles toward its southern limits, as the mountains recede from the coast. Extensive swamps line the coast in several places, and the soil near the sea-shore is frequently sterile; but farther inland the country improves, and contains many fertile tracts. The peninsula of Florida, which belongs to this region, is low and flat, and a large portion of it covered with swamps.

123. SOUTH AMERICAN PLAINS.-A great central plain stretches through the whole length of South America. It is divided into three principal portions-the plain of the Orinoco, the plain of the Amazon, and the plain of the Rio de la Plata,deriving their names from the three principal rivers by which they are respectively drained. These divisions are distinguished by the names of llanos, selvas, and pampas.

Venezue! and New Granada which extend to the north and west from the Orinoco. They have a very level surface, and so gently do they slope toward the sea, that a slight rise in the Orinoco reverses the current of the tributary streams. At the close of the rainy season the llanos are covered with luxuriant grass, and form rich pasture grounds; but during the dry months which succeed, the vegetation is entirely destroyed, and the parched ground opens in deep and wide crevices, giving the whole country the aspect of desolation and sterility.

125. The Selvas, or Forest Plains, extend over the lower portion of the basin of the Amazon, and within the limits to which the annual inundations of that river and its tributaries extend. A large part of this country is covered with dense forests.

126. Mrs. Somerville thus describes the selvas of South America:

"The soil, enriched for ages by the spoils of the forest, consists of the richest mold. The heat is suffocating in the deep and dark recesses of these primeval woods, where not a breath of air penetrates, and where, after being drenched by the periodical rains, the damp is so excessive that a blue mist rises in the early morning among the huge stems of the trees, and envelops the entangled creepers stretching from bough to bough. A death-like stillness prevails from sunrise to sunset; then the thousands of animals that inhabit these forests join in one loud, discordant roar, not continuous, but in bursts. The beasts seem to be periodically and unanimously roused by some unknown impulse, till the forest rings in universal uproar. Profound silence prevails at midnight, which is broken at the dawn of morning by another general roar of the wild chorus. Nightingales, too, have their fits of silence and song; after a pause they

Questions.-121. Into how many kinds may prairies be ranged? Describe the Bushy Prairies, the Dry, or Rolling Prairies, - the Moist, or Wet Prairies. 122. Describe the plain of the Atlantic coast. The peninsula of Florida. 123. Into how many portions is the great central plain of South America divided? By what names are they distinguished?

Questions.-124. Where are the Llanos situated? What is said of their level surface? How covered during the rainy season? Their aspect during the dry season? 125. Situation of the Selvas? How covered? 126 Mrs. Somerville's description of the selvas of S. America? 127. What are the Pampas? Describe the country between the 32d and 39th parallela

literally to render the country impassable. During nine months of the year the thistles are here the predominant (and almost the only) feature of the vegetable kingdom, but with the heats of the summer they become burned up, and their tall, leafless stems are leveled to the ground by the powerful blast of the pampero, or southwest wind, from the snowy ranges of the Andes, after which the earth is covered for a brief time with herbage. This is destined, with the return of spring, again to give way to the stronger vegetation, which it had succeeded, and for a time supplanted.

128. The plain which extends from the banks of the Negro (latitude 39° south) to the southern extremity of the continent is for the most part barren; in some places it is covered with sand, mixed with stones and gravel. It contains no trees, but a scanty vegetation of shrubs and herbage is found in a few hollows and ravines.*

part of the Alps, from Mont Blanc to the frontiers of Tyrol, there are reckoned more than 400 glaciers, some of them only 3 miles in length, while others are from 18 to 21 miles long, from 1 to 2 miles wide, and from 100 to 600 feet thick. Altogether the glaciers of Switzerland are estimated to cover a surface of upward of 1,000 square miles, and form a sea of ice from the inexhaustible reservoirs of which some of the principal European rivers are supplied.

VIEW OF A GLACIER.

130. Glaciers are not composed of solid ice, but consist of a mixture of ice, snow, and water. They owe their origin to the accumulation of the snow which falls from the sides of the mountains, and becomes only partially melted during the short summer of these elevated regions.

131. It is a remarkable fact respecting glaciers that they have an onward flow like rivers. The movement is very slow,

Questions.-128. Describe the plain which extends to the south of the Negro. 129. What is a glacier? Where do glaciers occur extensively? Where else are they common? Number of the glaciers along the central part of the Alps? Their extent?

Hughes' Manual of Geography.

+ GLACIER is from the Latin glacies, ice. The French word glaciere, from glace, signi files an ice-house.

MER DE GLACE, SWITZERLAND.

133. Glaciers, originating in the regions of eternal frost, descend far below the line of perpetual snow. The lowest limit to which perpetual snow extends downward in the Swiss Alps. is about 8,500 feet above the level of the sea. The lower glacier of the Aar descends more than 1,500 feet below the snowline, while others descend 4,000 or 5,000 below the region of perpetual snow and ice, as, for examples, the glaciers of the Upper and Lower Grindelwald.

134. The appearance of glaciers is thus described by Lyell : "When they descend steep slopes and precipices, or are forced through narrow gorges, the ice is broken up and assumes the most fantastic and picturesque forms, with lofty peaks and pinnacles projecting above the general level. These snow-white masses are often relieved by a dark background of pines, as in the valley of Chamouni; and are not only surrounded with abundance of the wild rhododendron in full flower, but encroach still

lower into the region of cultivation, and trespass on fields where the tobaccoplant is flourishing by the side of the peasant's hut."

Questions.-Number of square miles covered by the glaciers of Switzerland? 130 Of what do glaciers consist? Their origin? 181. Remarkable fact respecting glaciers? Rate of movement? In what part most rapid? Results obtained by Agassiz? 132. Upon what does the rate of motion depend? State the movement of the Mer de Glace at different seasons. 138. Do glaciers descend below the limit of perpetual snow? What is the lowest limit of perpetual snow on the Alps? To what distance below this line are glaciers known to descend? 131. Appearance of glaciers as described by Lyell?

135. Snow mountains and glaciers, though devoid of vegetation in the upper regions, and presenting a picture of desolation on a scale of magnificence which makes it awful, are yet a striking instance of the truth that nothing was made in vain.

"Herds of chamois are at home amid the frozen heights of the Alps; the Tibetian cow can only bear the climate of the valleys in winter; nor can man pronounce such districts barren, though cheerless in appearance, and

never intended for his residence. They minister to his comfort, happiness,

and even luxury, as the inexhaustible sources of those streams which in summer, when other waters are evaporated and dried up, roll on through the plains, fountains of fertility and plenty. The Rhone, Rhine, Po, Reuss, Ticino, Aar, Adige, Inn, and Drave, respectively flowing to the German Ocean, Mediterranean, Adriatic, and Black seas, are fed from the snows and glaciers of the Alps."-REV. THOMAS MILNER.

LESSON XII.

SNOW MOUNTAINS AND AVALANCHES.

136. THE polar regions are covered with fields of perpetual ice and snow. In the temperate and torrid zones everlasting frosts prevail only on the high lands. The elevation at which perpetual snow begins in these zones varies with the latitude. It is 16,000 feet from the level of the sea at the equator; 9,000 feet near latitude 45°; 5,000 feet at latitude 60°; 1,000 feet at latitude 70°; and about latitude 80° the line of perpetual snow comes down to the sea-level.

137. The principal localities of permanent snow in the torrid

MOUNT EGMONT.

and temperate zones are Iceland, Norway, the Alps, and Pyre. nees, in Europe; the Caucasus, Himalaya, Kuen-lun, and Altai mountains, in Asia; the range of the Greater Atlas, in Africa;

Questions.-185. What remark is made of snow mountains and glaciers? How illustrated? 186. Polar regions how covered? Where only do everlasting frosts prevail in the temperate and torrid zones? Elevation at which perpetual snow begins at the equator? At the 450? 600? 700? Snow-line at the 800? 187. Principal localities of permanent snow in the torrid and temperate zones? 188. Accumulation of snow masses? Where precipitated? Destructive effects?

and the Andes, and higher parts of the Rocky Mountains, in America. The mountains of South Australia, and Mount Egmont, in New Zealand, are snow mountains. The Himalaya derives its name, "the dwelling of snow," from the vast surface occupied by it.

138. The summits of these lofty mountains accumulate enorsurrounding valleys, producing terrible disasters. These demous masses of snow, which are often precipitated into the scending bodies increase in volume by the dislodgment of other masses, and fall with tremendous velocity and violence, uprooting trees, overwhelming houses and villages, and stopping the flow of streams and rivers.

139. Such falls are very common in Switzerland, where they are called avalanches,* or lavanges. In Norway they are called the snee-fond. Four kinds are noticed-drift, sliding, creeping, and ice avalanches.

140. (1.) A drift avalanche is the fall of the drifts and other accumulations of snow from the upper regions. During calm weather snow collects in enormous volumes on the declivities, where it remains until the wind forces it from its resting-place, and it rushes down into the lower regions. In its progress it forces off other masses, which augment its size, and becoming thus enlarged, it descends with constantly accelerated energy, occasioning as much damage by the whirlwind rush of the air as by the direct attack of the snow.

141. (2.) A sliding avalanche is a descent of snow masses which have become loosened by the heat of the earth. Avalanches of this class occur in spring, and commonly originate in the middle region of mountains. (3.) Creeping avalanches originate in a similar manner, but on less steep declivities. (4.) Ice avalanches are parts of a glacier, detached by the summer heat, or broken off by their own weight, on the extremity projecting over the edge of a precipice.

142. The following interesting description of avalanches is by the Rev. Thomas Milner:

"On descending the Sheideck into the valley of Grindelwald, canton of Berne, the extraordinary effects of an ice avalanche that fell some years ago are observable. The ground is entirely cleared; the trees have been swept away like reeds; an area of at least a mile and a half square is strewn with stones and stumps; a fine forest growing on each side of the area, which was untouched by the falling mass.

66

143. A similar avalanche descended near the village of Randa, in one of the valleys of the Valais canton, in 1819. It covered with ice, rubbish, and fragments of rock an area of 2,400 feet in length, by 1,000 feet wide, to the depth of 150 feet. It fell on an uninhabited spot, but the adjoining village was destroyed by the tremendous rush of the compressed air consequent upon the descent of such an enormous mass, about 9,000 feet. Beams of houses were carried nearly a mile into the forest, and the massive stone steeple of the church was snapped asunder.

144. "In the year 1749, a creeping avalanche of snow descended in the valley of Tawich, in the canton of the Grisons, and buried the whole village of Bueras, pushing it at the same time from its site. The catastrophe occurred in the night, and so stealthily, that it was unperceived by the inhabitants, who, on awaking in the morning, were surprised at the pro

longed darkness. Sixty out of a hundred persons were dug out alive, obtaining a sufficient supply of air through the interstices of the snow to sustain life.

Questions.-189. Where are such falls very common? What are they called in Switzerland? In Norway? What four kinds are noticed? 140. Describe the drift avalanches. 141. The sliding avalanches,-the creep ng avalanches,-the ice avalanches.

* AVALANCHE, from the French av ler, to descend..

Most High shall abide under the shadow of the Almighty.'"' verify the sacred declaration, He that dwelleth in the secret place of the preservation as an answer to his prayer; and to every pious mind it will through the snow, and reached Meyringen in safety, firmly regarding his sanctified by prayer. Its inmate with his dog succeeded in working his way thundering down, crushing every apartment but the one which was then accordingly into an inner room and began to pray, when the avalanche came. Suddenly the impression seized him to retreat into the hospice. He went grand catastrophe in the Alps-the noise of a mass disturbed and quivering. recurred again. It was one of those signals which frequently precede a no benighted wayfarer appeared on sallying forth with his dog. The sound terious sound in the evening, like the cry of a human being in distress; but occupied with his art of wood-carving, the solitary was alarmed by a mysgreat storm occurred, and the snow fell incessantly for four days. While with provisions and dogs, from November to March. In the latter month a well known to pilgrims in the Oberland, is only tenanted by a single servant remarkable preservation. The hospice, remote from any human habitation, 145. "In 1838 the secluded hospice of the Grimsel was the scene of a

Around what ocean are most of the volcanoes of the earth disposed?

On which side of the Pacific are they most numerous? Are
the volcanoes on the western side chiefly upon islands, or on
the mainland? What peninsula in the eastern part of Asia is
traversed by a chain of volcanoes? Through what islands is this
chain continued southward to the borders of the Indian Ocean?
Does it extend into the large island of Australia? Through
what part of the Australasian Archipelago is it prolonged, and
in what island does it terminate?

Are the volcanoes on the eastern side of the Pacific almost
wholly continental, or mainly insular? To what great chain
of mountains are they confined in South America? To what
one in North America? In which of the two grand divisions
are they most numerous? In what part of North America do
they abound chiefly upon the mainland?

What chain of islands on the northern border of the Pacific
contains a large number of active volcanoes? To what grand

division

does this chain belong?

Of the highlands of what vol

canic peninsula does it form a continuation? What groups of islands in the central Pacific are seats of active volcanoes?

Are these volcanoes distributed in lines like those along the
shores of the continent, or do they appear to be independent
centers of volcanic action?

Is there any great belt of volcanoes surrounding the Atlantic
like that around the Pacific? Are there any volcanic peaks on
the mainland, near the Atlantic? To what chain of small
islands are the only volcanoes on the west of this ocean confined?

What remarkable volcanic island on the northern border
of the Atlantic? What island northeast of this contains the
most northern volcanoes known on the globe? What three
groups of islands on the eastern side of the Atlantic are seats
of active volcanoes?

On the northern borders of what sea connected with the
Atlantic are there several volcanoes? To the islands near the
southern part of what peninsula are they mostly confined?
What celebrated volcano on the mainland of Italy?

What sea and what bay on the northern borders of the Indian
Ocean contain islands which are seats of active volcanoes?
What island east of Madagascar has an active volcano? Are
there any volcanoes known on the mainland of Africa? What vol-
cano in Victoria Land is the most southern known on the globe?
Which is the only grand division containing volcanoes far in

Are the volcanic regions of the globe generally subject to
earthquakes? Do earthquakes appear to be common in the
regions farthest removed from volcanic sites?

[It will be borne in mind that the above map, being drawn on Mer-
cator's projection, greatly magnifies the distances in the higher latitudes.]
What grand division of the Eastern Continent, which is free
from volcanoes, is also mostly free from earthquakes? Do
earthquakes prevail in the eastern part of South America? In
the northeastern part of North America? Of Europe? In

LESSON XIII.

VOLCANOES.

sometimes entire, like the walls of a circus, but more commonly at their summit, called the crater, or cup, the sides of which are 147. Volcanoes are generally of a conical shape, with a hollow

only, and which are hence called Mud Volcanoes. lava: it is also applied to mountains having eruptions of mud sides, flame, smoke, ashes, and streams of melted matter called to those mountains which send forth, from their summits or ancient Romans gave to their imaginary god of fire) is applied 146. THE term volcano (derived from Vulcanus, the name the

states of volcanoes? Stromboli? Examples of intermittent volcanoes? What are extinct pearance? The general appearance of the bottom or floor of craters? 148. The three 147. General shape of volcanoes? What is the opening at the summit called?. Its ap Questions.-146. From what is the term volcano derived?

tent, or extinct. seas, but very rarely violent. Etna, Vesuvius, and Cotopaxi history, a permanent fiery beacon to the sailors of the adjoining It has been uninterruptedly active from the dawn of authentic Mediterranean—a comparatively lowly mound, 2,175 feet high. 148. Volcanoes are either continuously active, or intermit of smoke, steam, and flame issue at the most tranquil intervals. Of the former class is Stromboli, in the of ashy cones, with cracks and fissures, through which jets rent. The bottom or floor of craters usually presents a series To what is it applied?

volcanoes? Instance.