28 



INTRODUCTION. 



valleys, lakes disappear, and rocks and islands rear their wet summits from the bosom of the 

 foaming sea. 



6. Valleys. The spaces which separate one mountain from another, or one cham from 

 another, are called vallnjs, and their lowest part is generally the bed of a river, which rises in 

 the higher grounds, or of a lake. The term valley is also applied in a wider sense to the whole 

 extent of country drained by a river and its branches. 



7. Plains. The surface of the earth seldom forms a perfect level for any great extent ; it 

 has a more or less perceptible inclination, generally rising from the coasts towards the interior, 

 and even those regions which are described as plains, have an undulating surface. In some 

 mstances there are extensive plains of great elevation, called plateaux or table-lands, the de- 

 scent from which to the low countries, exhibits to the inhabitants of the latter the appearance 

 of a long chain of mountains. 



8. Deserts, Steppes, &c. Tliere are vast tracts consisting merely of wide plains of sand or 

 shingle, or occasionally broken only by bare rocky heights, destitute of water and vegetation, 

 and shunned equally by man and beast ; these are called deserts. Interspersed over these 

 oceans of sand, we sometimes lind fertile spots, watered by springs and covered with trees, 

 called oases. In some places we meet with vast plains entirely destitute of trees, out bearing 

 grasses, saline and succulent plants, and dwarfish shrubs. Those which bear nutritive herbage 

 are called prairies, llanos, or pampas ; while those which have a scanty, and often only a tern- 

 norarv vegetation, are called steppes or karroos. 



V. LAKES AND RIVERS. 



IVinnipiseogce Lalic, J^ew Hampshire. 



1 . Lakes. An inland body of water not immediately connected with the ocean or any of 

 its branches, is called a lake ; but some bodies of this description are also commonly called 

 seas. They are generally fresh, but are salt when situated in districts of which the soil contains 

 saline matter. 



2. Classes of Lakes. There are four sorts of lakes. (1.) The first class includes those 

 which have no outlet and receive no running water ; these are usually very small. 



(2.) The second class comprises those which have an oudet, but which do not receive any 

 running water. They are geneially in elevated situations, and are often the sources of large 

 rivers ; they are formed by springs rising up imo a large hollow, until the water runs out over 

 the lowest part of the edge of the basin. 



(3.) The third class embraces those lakes which receive and discharge streams of water, 

 and is the most numerous. These lakes are the receptacles of the waters of the neighboring 

 country, but in general have but one outlet which bears the name of the principal river that 

 enters the lake. Such a river is said to traverse or flow through the lake, though not with 

 strict propriety, since its current -'s commonly lost in the general mass of waters, and the outlet 

 IS in fact a newly formed river. The largest lakes of this class are the great lakes which lie 

 on the northern frontier of the United States, and of which the St. Lawrence is the only outlet 

 to tlie sea. 



