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Introduction to Geology. 
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 
by the a action of the elements, the w earing away of strata by 
torrents, the deposition of decayed vegetabl le matter, peat, and 
coze; 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 fhe 
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 none 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 the mouths of great rivers, and on flat 
shores, the effects of alluvial oper rations upon the earth, as 
compared with the diluvial, are inconsiderable, and have pre- 
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 disappear ed, and are now strangers to 
the soil of which they former ly were the principal occupants. At 
the same time, these animals, for the most part, belonged toa 
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 :— that whilst alluvium is of comparatively modern origin, 
whilst it contains the remains of existing beings, among which 
the fossils of more ancient times are Somer anee 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 Mdinbur: oh 
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.” 
