274 ALLUVIAL FORMATIONS. 



XVIIL 



§ IV. ALLUVIAL FORMATIONS. 



By this term are designated those accumulations of sand, clay, gravel, 

 rounded flints, and other water- worn materials, that cover the surface of 

 the regular formations, and are composed either of the detritus of the 

 upper portions of the strata on which they repose, or of heaps of materials 

 confusedly mixed together, transported from distant or more elevated 

 regions. These beds are consequently as various as the strata from 

 whence they are derived, and it is neither possible, nor necessary, to 

 enumerate every difference in their appearance, and composition. 



As monuments of the last revolutions that have swept over the face 

 of the earth, their study becomes peculiarly interesting; for although 

 most of them may be regarded as recent depositions, when compared with 

 the formations previously examined, yet even the latest will be found to 

 exhibit indisputable evidence of a very remote origin. 



The beds usually comprehended under the general name of Alluvium 

 may be more properly separated into two divisions, viz. : 



1. Diluvium, consisting of gravel, boulders, sand, &c. produced by 

 causes no longer in action. 



2. Alluvium, strictly so called, composed of the mud of rivers, deltas, 

 the gravel of torrents, &c., the effect of causes which still continue in 

 activity *. 



* " It will be convenient if geologists will consent to restrict the term Diluvium to the super- 

 ficial gravel beds produced by the last universal deluge; and designate by the term Alluvium, 

 those local accumulations that have been formed since that period by torrents, and rapid 

 rivers, the bursting of alpine lakes, and similar minor causes, which operate daily, and partially, 

 within the sphere of our own observation." Professor Buckland, Geolog. Trans. Vol. v. p. 333. 



