They are formed by the union of brooks and rivulets, whose collected waters they discharge into the sea, or into some great inland lake.

Q. What is the basin of a river?

A. The whole extent of country from which the waters of a river are drawn, or which it drains, is called its basin. Q. What is a watershed?

A. The elevated land which separates one basin from another.

Q. On what circumstances does the size of a river depend?

A. On the surface or extent of its basin, on the number of springs existing in that surface, and the degree of moisture possessed by the climate of the region from which the river draws its supplies.

Q. Where are the largest rivers in the world to be found?

A. In North and South America.

Q. To what circumstances is it owing that North and South America possess larger rivers than any other part of the globe?

A. To the peculiar position of the principal ranges of mountains in North and South America, those ranges being much nearer to the Pacific than to the. Atlantic coast; to the circumstance of the largest portion of its running waters being drained towards the Atlantic; and to the number of springs that exist in the two countries.

Q. Why has not Europe such large rivers as either North or South America? A. Because Europe is not so large as either North or South America.

Q. Why has not Africa such large rivers as either North or South America?

A. Africa has a very hot climate, and abounds in sandy deserts.

Q. Why has not Asia such large rivers as either North or South America?

A. In Asia the atmosphere is not, in general, so moist as in North and South America, while the more central position of the principal mountain range of that continent, and the existence of the inland

lakes, the Caspian Sea and Lake Aral, which are the final receptacles of the rivers which fall into them, are the causes why the waters are more equally drained off in different directions than in the new world.

Q. What causes the overflowings of the Nile, in Egypt?

A. The fall of rain in the mountains of Abyssinia, in the interior of Africa, where one of the branches of the Nile rises. Q. What is a lake?

A. A lake is water surrounded with land.

Q. How many descriptions of lakes are there?

A. Four-1st. Lakes which have no outlet, and which do not receive any running water. 2nd. Those which have an outlet, but which do not receive running water. 3rd. Those which have an outlet, and also receive running water, as the large lakes in North America; and, 4th. Those which have no outlet, but which receive running water, as the Caspian Sea and Lake Aral.

Q. What is an earthquake?

A. Sometimes earthquakes are no more than a slight trembling of the earth; at other times they are so violent that the earth opens, and, in doing so, has destroyed whole cities with their inhabitants.

2nd.

Q. How many different kinds of movements are there in the waters of the sea? A. Three-1st. The waves. The tides. 3rd. The currents. Q. What are waves caused by? A. By the action of the winds on the surface of the water.

Q. Does the agitation of the water, which is caused by the winds, extend far below the surface of the water?

A. In the roughest weather, the sea is said to be calm at the depth of ninety feet.

Q. What are the tides caused by?

A. They are caused by the attraction of the sun and moon on the waters of the ocean; but principally by the attraction of the moon.

Q. What are currents caused by?

A. They are caused by the wind; by the tides; by a difference in temperature between two parts of the sea; by evaporation; and by the rotation of the earth on its axis.

Q. What effect does a north-west wind of any lengthened duration produce on the Baltic Sea ?

A. It causes the Baltic Sea to rise two feet and upwards above its ordinary level.

Q. How are currents produced by the tides ?

A. The rise and fall of the tides frequently cause alternate currents in opposite directions. These currents are very striking near islands, such as the Orkney and Shetland Isles. In open seas, the rise and fall of the tides is much less than in contracted seas.

Q. How is the existence of currents in the ocean, from the poles to the equator, shown?

A. By masses of ice floating from the frigid to the temperate regions. Icebergs drifted from the North Pole have