388 THE FOOT-HILLS OF MOUNTAINS. 



inequalities with which the earth's surface is studded. 

 Hence it appears to follow that the great mountain 

 chains of the world were in all probability, originally 

 much higher and more abrupt in their slopes than they 

 are at present, as the constant falls of material must, 

 in the course of ages, have caused considerable alterations 

 to have taken place in their contours. This wearing 

 away of the higher peaks has also of course tended to 

 fill the valleys with a level floor of detritus covered 

 with deep alluvial soils, such as we find so often to 

 exist between the spurs and parallel ranges of mountain 

 chains large quantities of these materials again, have 

 been carried down into the plains, in the form of gravel, 

 sand and mud, by the streams which are generally 

 found to occupy the beds of nearly all extensive valleys 

 and ravines. 



Consequently the foot-hills extending along the bases 

 of great mountain ranges are always found to consist 

 of long slopes formed of deposits of such materials. 

 In many places such foot-hills are covered with luxuriant 

 forest growths. Lands of this kind, in their natural 

 state, possess great fertility, on account of the depth 

 and richness of the soil washed down upon them from 

 the hill sides above. Consequently therefore, inasmuch 

 as great wealth of vegetation always goes hand in 

 hand with the existence of malaria, in tropical regions, 

 these localities are in most cases hotbeds of per- 

 nicious fevers of malarial type in warm climates, 

 and some of the most deadly neighbourhoods in the 

 world occur under such conditions. The wide district 

 known as the " Terai " will probably present itself to the 

 minds of our Indian friends, as a striking instance in point. 



The Terai (including the Bhabar) is a belt of fertile 



