626 



SCIENTIFIC RECREATIONS. 





and the heat of the valleys, which are naturally closely connected with the 

 upheaval of mountain ranges. We have already spoken of the never-ceasing 

 influences of the air and water upon the rocks, and we need say little about 

 valleys. There are valleys of dislocation, denudation, and undulation. The 

 great valley of Western Asia, wherein lie the Caspian and Aral seas, seems 

 to have been caused by the upheaval of the Caucasus and the Persian plateau. 



PLAINS are very varied. We have European Heaths and Landes ; 

 American Savannahs, Prairies, and Pavipas ; Asian Steppes, and African 

 Deserts. All of these possess certain features in common, more or less 

 vegetation, and sometimes absolute sterility. 



PLATEAUS, or Tablelands, are 

 elevated plains frequently undulating 

 in character. The Plateau of Bolivia 

 is 13,000 feet high, and extends 

 along by the Andes. The tableland 

 of Quito is nearly 10,000 feet high, 

 and borders on the giants Cotopaxi 

 and Chimbarazo. 



Rivers and lakes add not only 

 to the wealth of nations by their 

 usefulness, but, by the additional pic- 

 turesqueness of their appearance, to 

 j| the beauty of the landscape. The 



djIJlL- ffl IPl ve l c ity of rivers would be very much 

 increased if it were not for the strong 

 resistance offered by the banks and 

 the stones to the current, and by fric- 

 tion. The Rhine and the Rhone, if 

 thus unimpeded, would flow at a rate 

 considerably over one hundred miles 

 an hour ; and our own little stream 

 (the Thames), instead of eddying 

 peacefully and twirling gracefully by 

 Medmenham or Cookham, would rush along at the speed of the train which 

 so often crosses it on its way to the sea. 



The slopes of river-beds, like the slopes of mountains, vary very con- 

 siderably, and the inclination of a river varies at different places ; in a dis- 

 tance of seven hundred miles the Amazon only falls twelve feet, and the 

 current flows chiefly by impetus already acquired. A slope of one foot in 

 two hundred precludes all navigation, and at still greater inclines rapids and 

 cataracts are formed the great falls wearing away the river-bed by degrees ; 

 so it is calculated that hundreds of years ago Niagara Fail was much 

 farther down the river, and the cataract is slowly moving up stream. In 

 time, as the rock wears away, the height will disappear as the celebrated 

 " Falls," and will become a rapid within a few miles oi the lake. 



Fig. 713. The Staubbach (Lauterbrunnen), 



