§ 22. FORMATION OF FLUVIATILE STRATA. 59 



fluviatile sediments, readily determine the characters of 

 the fauna and flora of the countries through which the 

 rivers had flowed. We may here observe, that in tropical 

 regions, where animal life is profusely developed, and but 

 little under the control of man, the animal remains buried 

 in the deltas are far more abundant than in those of 

 European countries, which are thickly peopled, and in a 

 high state of civilization. The enterprising but unfor- 

 tunate Lander informed me, just before he embarked on 

 his last and fatal expedition to Africa, that many parts of 

 the Quorra, or Niger, so far as the eye could reach, teemed 

 with crocodiles and hippopotami ; and so great was their 

 number, that he was often obliged to drag his boat on shore 

 lest it should be swamped by them. 



It is unnecessary to dwell longer on these operations ; it 

 will suffice to have shown, that by the simple effect of 

 running water, great destruction and extensive modifica- 

 tions of the surface of the land are everywhere taking 

 place, and at the same time fluviatile deposits are forming 

 on an extensive scale, and imbedding animal and vegetable 

 remains. Thus, in the deltas of the rivers of England are 

 found the bones and antlers of the deer, horse, and other 

 domesticated animals, associated with the trunks and 

 branches of trees and plants, river and land shells, human 

 bones, and fragments of pottery and other w r orks of art : 

 while in those of the Ganges and the Nile, the remains of 

 the animals and vegetables of India and of Egypt are 

 respectively entombed. 



22. Formation of fluviatile strata. — There is a 

 circumstance connected with these facts which it is neces- 

 sary here to consider. The quantity of water in streams 

 and rivers varies considerably at different periods of the 

 year ; in the rainy season the rivers are overflowing, and 

 the waters remarkably turbid : consequently the deposits 

 are much greater at those periods than in the summer 



