338 The Realm of Nature CHAP. 



flooding the sunk plains of arid regions, so as to provide 

 new sea-routes, or modify desert climate by the presence of 

 a sheet of water. Examples of these are the proposal to 

 admit the Mediterranean and Red Sea to the great Jordan 

 Valley ( 335), in order to open a new sea-route to India ; 

 and the suggestion of admitting the Mediterranean water to 

 some of the shotts of the northern Sahara ( 377). Land- 

 masses necessitating long sea-routes have frequently been 

 severed by artificial channels, of which the Suez Canal is 

 the most remarkable example. A German canal for large 

 vessels across Jutland, from the North Sea to the Baltic, is 

 in progress ; a French canal to admit war-vessels is about 

 to join the Bay of Biscay and the Mediterranean north of 

 the Pyrenees ; a Greek canal has severed the isthmus of 

 Corinth. Several attempts have been made to cut the 

 isthmuses of Central America and have hitherto failed, not 

 because the task is impossible, but on account of financial 

 or political bungling. Rivers are continually being inter- 

 fered with, their mouths deepened into harbours, their 

 course levelled into canals, the current split up into irriga- 

 tion channels, or diverted bodily to prevent floods, or to 

 furnish a route for railways. The greatest project of river 

 diversion ever proposed is that of a Russian engineer to 

 restore the Oxus to its ancient bed ( 382) and bring it 

 into the Caspian once more, thus affording a water-way 

 from Europe into Central Asia. Tunnels such as those 

 through the Alps, through the Khojak Hills in North-western 

 India, and under the Andes in South America, are other 

 examples of geographical changes wrought by human power. 

 So too are the subsidences which follow mining operations, 

 and sometimes alter the direction of streams. 



433. Biological Changes. By diligent cultivation and 

 careful selection the food-grains of the modern farmer have 

 been produced from various species of wild grasses, which 

 naturally had small and innutritious seeds. In like manner 

 many varieties of animals have been obtained by careful 

 breeding, which are specially fitted for the use of man. 

 Without his interference they would never have existed, 

 and in many cases, if left to their own devices, they would 



