Litroductio7i to Geology, 77 



Alluvium, 



Alluvium is understood to designate those accumulations of 

 earth, gravel, sand, and other loose materials which result 

 from causes in daily operation. These materials are derived 

 partly from diluvium, partly from the decomposition of rocks 

 }3y the action of the elements, the wearing away of strata by 

 torrents, the deposition of decayed vegetable matter, peat, and 

 ooze ; from shifting sand-banks at sea, and blown sand on 

 shore, and even from the operations of man. Of this class are 

 the deltas which are produced by sedimentary subsidence ; 

 and of the same character is that formed at the mouth of the 

 Mississippi, on the most gigantic scale that our globe exhibits, 

 from the forests of timber which have floated, during the lapse 

 of ages, down that mighty stream. In short, it defines all 

 deposits formed since the deluge, as distinguished from those 

 accumulated through diluvial agency. 



Except under certain circumstances, such as the formation 

 of low tracts of land at tlie mouths of great rivers, and on flat 

 shores, the effects of alluvial operations upon the earth, as 

 compared with the diluvial, are inconsiderable, and have pro- 

 duced slight alteration from the remotest period. 



Some of these depositions contain traces of the work of man, 

 such as rude implements, canoes, &c., and skeletons of some 

 animals, which, in the lapse of ages, as population and cultiva- 

 tion extended, gradually disappeared, and are now strangers to 

 the soil of which they formerly were the principal occupants. At 

 the same time, these animals, for the most part, belonged to a 

 different class from those which are traced in the diluvial de- 

 posits, and the subterranean caverns. The first class, in almost 

 all cases, is strictly identical with existing species, under 

 similar climates, and includes the human race. The other ani- 

 mals either approach in resemblance to those which exist only 

 in tropical climates, or are entirely unknown in a recent state, 

 and are wholly unmixed with traces of man and his operations. 

 The essential difference in these two deposits, therefore, is 

 this : — tlnit wliilst alluvium is of comparatively modern origin, 

 whilst it contains the remains of existing beings, among which 

 the fossils of more ancient times are sometimes fortuitously 

 introduced, the genuine undisturbed diluvium contains no 

 such admixture, but the latter only. Hence the relative ages 

 of these accumulations of detritus are fully and clearly ascer- 

 tainable. In a recent controversy, conducted in the Edinburgh 

 Philosophical Journal^ Dr. Fleming has opposed this hypo- 

 thesis of Baron Cuvier and Dr. Buckland, and refers the ex- 

 tinction of these early quadrupeds, not to a deluge, but " to 

 the destructive influence of the chase." 



