ALLUVIUM. 



ALLUVIUM. 



materials into lakes, we cannot have a more 

 favourable opportunity than in Switzerland. 

 Many of the lakes of this sublime and majestic 

 country are rapidly filling from this cause; 

 and in some of them water plants are seen 

 above the surface of the water. But when a 

 river suffers inundation, the earthy matter, 

 which is held in mechanical mixture, is ar- 

 rested, and deposited on the land that is over- 

 flowed, and a richly productive soil is formed. 

 One or two examples may illustrate these re- 

 marks. 



The Ganges annually overflows its banks, 

 and deposits a rich alluvial soil over the 

 country it inundates. This magnificent river 

 was supposed to take its rise on the northern 

 side of the Himalaya mountains, until it was 

 proved, in 1819, by Lieutenant Webb, that all 

 the streams which unite to give its existence, 

 take their rise on the south side of the Hindoo 

 Coast, or Snowy Mountains. The melting of 

 the snows, and the heavy periodical rains aug- 

 ment the volume of the water, and by the end 

 of June, before the rainy season has com- 

 menced in the low country, the river has ge- 

 nerally risen fifteen feet; but after the rains in 

 Bengal it usually attains a height of thirty-two 

 feet above its ordinary level. By the end of 

 July all the low countries adjoining the Ganges 

 and the Burrampooter are overflowed, and no- 

 thing but houses and trees are seen for many 

 miles inward. The province of Bengal is 

 divided into two nearly equal parts by the 

 Ganges ; and as a large portion of the country 

 on the banks of the river is low, it is especially 

 exposed to inundation, from which circum- 

 stance it probably derives its name, such dis- 

 tricts being called beng. A deep bed of rich 

 soil is deposited during the period of the over- 

 ilow, and the vegetable productions are of the 

 most varied and luxuriant character. Rice, 

 wheat, barley, tobacco, indigo, cotton, the mul- 

 berry, and the poppy, are all cultivated with 

 success on the alluvial soils. 



It is well known that Egypt has been from 

 time immemorial indebted to the overflow of 

 the Nile for a rich alluvial soil, as well as for 

 the means of irrigating the land. The an- 

 cients seem to have been altogether at a loss 

 to account for the periodical overflow of this 

 river ; and when we consider the appearances 

 before them, we are not surprised at the diffi- 

 culties they experienced. They observed it in 

 a country that was not moistened by a drop of 

 rain, and where it was unaided by a single 

 stream, and yet, at its stated period, it began 

 to lift iis waters from their bed, and rising 

 higher and higher, overflowed its banks, and 

 spread itself like a sea over Lower Egypt, re- 

 freshing the parched earth with moisture, and 

 aiding its productiveness with the formation 

 of a superficial covering of rich loam. The 

 philosophers speculated without success upon 

 its cause ; but while they were disputing as to 

 the origin of the phenomenon, year by year 

 the Nile rose, and left the evidence of its be- 

 neficial sway in the richness of the crops and 

 the luxuriance of the country. From the in- 

 vestigations that have now been made, we 

 know that the rise of the Nile is occasioned 

 by the rains which fall on the high mountains 



in the interior and tropical regions, and not, as 

 many of the ancients supposed, from the Ete- 

 sian winds, which, blowing periodically from 

 the north, prevent the waters from reaching 

 the sea. 



The great importance of rivers, as agents in 

 the production of alluvial soils, cannot be 

 more strongly proved by any positive evidence 

 than by a consideration of the state of Austra- 

 lia, a country remarkable for the fewness of 

 its rivers, and the general poverty of its soil. 

 Contrary to all precedents, the richest soils in 

 this land, excepting the alluvial, are found on 

 the summits of hills. The fires which so fre- 

 quently happen on the plains, the peculiar 

 character of the vegetation (chiefly consisting 

 of ever-greens), and the sparing distribution 

 of water, are the principal causes of the steri- 

 lity of this otherwise desirable country. There 

 are, however, spots which, covered with allu- 

 vial soil, can rival the richest and most culti- 

 vated districts of England; and the compari- 

 son of these with other lands impresses the 

 r the more strongly with the great im- 

 portance of the natural provision for the resti- 

 tution of that portion of the earth inhabited by 

 in ui i, by the deposition of new earthy matter 

 and a virgin soil. The alluvial flats of the 

 Nepean, the Hawksbury, and the Hunter 

 are spoken of by all writers as remark- 

 able for their fertility. The rich valley in 

 which the Lake Alexandrina is situated may 

 be noticed as another example of the influence 

 of alluvial soils. The country around this 

 lake appears to be one of the most beautiful 

 and fertile in Australia ; and a glance at the 

 map will immediately inform the inquirer of 

 the cause. It is so situated as to receive the 

 worn materials of the mountain chain that 

 ranges along the promontory of which Cape 

 .If TV is is the southern point, and also to obtain 

 moisture at all times from the lake, and a re- 

 novating soil whenever it may overflow its 

 banks. 



Alluvial soils are produced by the discharge 

 of mountain streams ijito valleys, as well as by 

 the overflow of rivers. We have already ex- 

 plained the manner in which they collect the 

 superficial covering of mountainous districts, 

 and being charged with earthy matter, bring it 

 into the plains. This may be deposited before 

 the streams are united together in an individual 

 channel as well as after, and should this be 

 done, the valley may be covered with alluvial 

 products. The formation of a river is a pro- 

 cess which requires time, and many changes 

 must happen before the flowing waters can 

 form for themselves a local habitation ; obsta- 

 cles must be removed, a bed must be scooped 

 out, and an outlet must be formed, in the per- 

 formance of which earthy matter must be ac- 

 cumulated, and extensive deposits be formed. 



A third cause in the production of alluvial 

 deposits may be mentioned. The sea is mak- 

 ing great inroads upon many of its shores, 

 carrying on a destructive war against the 

 cliffs that vainly endeavour to oppose its force; 

 while on the other hand it is in some instances 

 receding from the shores against which it once 

 i beat ; and thus, as though to recompense man 

 for what it takes away, gives to him a portion 



