SYLLABUS. SYLLABUS. ——-0 900 Water is formed by the union of oxygen and hydrogen. The waters of the earth may be divided into two classes —the continental and the oceanic. Water is asolid at and below 32° Fahr., a liquid from 32° to 212°, and a vapor above 212°. It passes off as vapor, however, at all temperatures. A pint of water is heaviest at the temperature of 39.2° Fahr. Hence in deep lakes, covered with ice, the lower layers of water are 7.2° Fahr. above the freezing-point. Large bodies of water moderate the extremes of tem- perature, because water takes in more heat while warming and gives out more.on cooling than any other common substance. 5 During the freezing of a body of water, or the condensa- tion of a mass of vapor, considerable stored heat-energy appears, or latent heat becomes sensible and warms the surrounding air. After a body of water has been cooled to the tempera- ture of 32° Fahr., it has still 142 heat-units, or pound-de- grees, to lose before it can turn into ice. After a body of ice has been warmed to the temperature of 32° Fahr., it has still 142 heat-units, or pound-degrees, of heat to gain before it can turn into water. Therefore, both freezing and melting are gradual pro- cesses. The rains cleanse the surface of the earth and purify the atmosphere. Water is necessary for the existence of life. It forms the main food of both animals and plants. The atmospheric waters are drained into the ocean either by surface or subterranean drainage. Springs are the outpourings of the subterranean waters. Springs may be classified according to peculiarities in the size, shape, and depth of their reservoirs, and the -nature of the mineral substances composing the strata over which the waters flow or in which they collect. According to the size of their reservoirs, springs are either constant or temporary. If their reservoirs have siphon-shaped outlet tubes, their discharges are periodical. When their reservoirs are superficial, springs are cold ; when deep-seated, they are hot or thermal. Springs whose waters are moderately cold have their reservoirs near the surface. Their lower temperature is due to their waters being shielded from the sun. Springs with very cold waters have their sources in the melting of large masses of ice or snow. Hot or thermal springs owe their high temperature to the heat they receive from the interior of the earth. Geysers are boiling springs, which, at irregular intervals, shoot out huge columns of water with great violence. The most extensive geyser regions are those of Iceland, - New Zealand, and Wyoming. Calcareous springs contain lime; silicious, silex; sul- phurous, sulphuretted hydrogen and metallic sulphides or sulphates; chalybeate, iron; brines, common salt; acidu- lous, carbonic acid ; petroleum, coal oil; bituminous, pitch. Rivers are fed both by surface and subterranean drain- age. : The main stream with all its tributaries and branches is called the river-system. The territory drained into the river-system is called the river-basin. The ridge or ele- vation separating opposite slopes is called the water-shed. In the upper courses of rivers erosion occurs mainly on the bottom of the channel; in the lower courses, at the sides. In the lower courses of rivers extensive flats or plains are found. They are caused by the erosion of the banks and the subsequent deposition of fine mud during inunda- tions. Rivers are constantly at work carrying the mountains toward the sea. Through their agency the mean height of the continents is decreasing, and their mean breadth. increasing. The eroded material, or silt, may accumulate—1. In the channel of the river; 2, Along the banks, on the alluvial flats or flood-grounds; 3. At the river’s mouth; and 4. Along the coast, near the mouth. The accumulations in the channel of the lower Missis- sippi have so raised the bed of the stream as to necessitate the erection of levees or embankments along the sides. Where the tides are weak and the ocean currents absent or feeble, the eroded material, or silt, accumulates at the mouths of rivers in masses termed deltas. The Alps are drained by the Rhine, the Rhone, the Po, and the Danube; these rivers have extensive delta-forma- tions. The plateau of Thibet is drained by the Hoang-Ho, the Yang-tse-Kiang, the Ganges, the Brahmapootra, and the Indus; all these rivers have extensive delta-formations. Among other extensive deltas are those of the Missis- sippi, which drains the long slopes of the Pacific and Appalachian mountain-systems; the Nile, the Tigris, the Euphrates, and the Zambezi. Fluvio-marine formations occur along the coasts; they are caused by the combined action of the river and tides. The destruction of forests, by increasing the rapidity of drainage, increases the violence of floods. Lakes along the river-courses decrease their violence, by allowing the torrents to discharge their waters. The direction of the drainage of a country is dependent on the direction of its slopes. The central plain of North America is drained north into the Arctic Ocean through the Mackenzie; east into the Atlantic through the Nelson and the St. Lawrence; and south into the Gulf of Mexico through the Mississippi. The central plain of South America is drained north into the Caribbean Sea through the Magdalena, east, into the Atlantic through the Orinéco and the Amazon, and south, into the Atlantic through the Rio de la Plata. The. rivers draining the great low plain of Europe rise either in the Valdai Hills or on the northern slopes of the predominant system. Asia possesses the most extended system of inland drainage of the continents. Extended systems are also found in. North America and Europe. The Atlantic and the Arctic Oceans drain about three- fourths of the continental waters. 3 The largest systems of fresh-water lakes occur in North America and Europe. The Great Lakes of North America occupy remarkable depressions in the continent. The beds of some of them are several hundred feet below the level of the sea. Lakes without an outlet are salt, because the waters they receive contain small quantities of saline ingredients, while the waters they lose contain none, i 4 ~~ \