Ch. XI.] NEWER PLIOCENE ALLUVIUMS. 145 



with the same ochreous clay which envelops the osseous remains 

 of higher antiquity *.' 



NEWER PLIOCENE ALLUVIUMS. 



Some writers have attempted to introduce into their classi- 

 fication of geological periods an alluvial epoch, as if the 

 transportation of loose matter from one part of the surface of 

 the land to another had been the work of one particular period. 

 In our opinion, they might have endeavoured, with equal 

 propriety, to institute a volcanic period, or a period of marine 

 or fresh-water deposits. We believe, on the contrary, that 

 alluvial formations have originated in every age, but more 

 particularly during those periods when land has been raised 

 above its former level, or depressed below it. We defined 

 alluvium to be such transported matter as has been thrown 

 down, either by rivers, floods, or other causes, upon land liable 

 to inundations, or which is not permanently submerged beneath 

 the waters of lakes or seasf. As examples of the other causes 

 adverted to in the above definition, we might instance a wave 

 of the sea raised by an earthquake, or a water- spout, or a 

 glacier. 



We have said permanently submerged in order to distin- 

 guish between alluviums and regular subaqueous deposits. 

 The latter are accumulated in lakes or great submarine re- 

 ceptacles, the former in the channels of rivers and currents, 

 where the materials may be regarded as being still in transitu, 

 or on their way to a place of rest. There may be cases where 

 it is impossible to draw a line of demarcation between these 

 two classes of formations, but these exceptions are rare, and 

 the division is, upon the whole, convenient and natural, the 

 circumstances being very different under which each group 

 originates. 



Marine alluvium. The term ( marine alluvium ' is, perhaps, 

 admissible if confined to banks of shingle thrown up like the 



* Journ. de Geologic, tome iii. No. x. p. 165. 



f Vol. ii. chap. xiv. 

 VOL. III. L 



