ON THE ALLUVIAL DEPOSITS. 371 



times deposited by the casual force of torrents or inun- 

 dations, independently of these more regular results ; 

 a circumstance aided by the diminished weight of stones 

 when in water, and often exciting wonder in those who 

 are not aware of this necessary fact. If these are other 

 irregularities, they may be attributed to lateral streams 

 or temporary floods. This regular procedure can not 

 however be traced in all rivers ; so, that, while some 

 terminate in the sea during their full vigour and flow, 

 others present only the appearances which belong to 

 the last stage. 



With such and other variations on which I need not 

 enlarge, the sections of a river alluvium present marks 

 of stratification, not always horizontal, by which, as I 

 have already said, they may be distinguished from an- 

 tient deposits, even where no river now flows. Yet, as 

 many rivers have originally met the sea or a lake, at 

 points far higher than their present junctions, their al- 

 luvia are often modified by actions that might easily be 

 overlooked. They sometimes also enclose strata of 

 peat or vegetable soil, formed during a period of repose, 

 in a plain or on the margins of a lake, and afterwards 

 overwhelmed bv inundation. Hence also we account 



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for the presence of organic remains, and, sometimes, 

 even of marine ones, far removed from the present sea. 

 It is superfluous to say that the nature of the fragments 

 must correspond with those of the rocks in which their 

 streams arise or through which their early progress lies, 

 except in the case of the passage of these through an 

 antient alluvium. 



The superficial features of river alluvia are often mo- 

 dified by the passage of streams, or by occasional inun- 

 dations ; and hence many intricate appearances, which 

 have caused them to be referred to " diluvian" sources. 

 Such are, terraces, hillocks, and other irregularities; 



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