ALLUVIA. 623 



the causes which produced a great portion of 

 them ; and that in consequence of these daily 

 actions, the alluvia of a general nature are often 

 in danger of being confounded with those of 

 more recent and partial origin. 



Many of the alluvial deposits present an alter- 

 nating stratification, more or less frequent and 

 regular, of the different modifications of which 

 they are formed, often emulating, in every thing 

 but consolidation, the finer and coarser beds of 

 the red sandstone. They also, in some places, 

 alternate with beds of peat, or of those sub- 

 stances called lignite or brown coal, which are 

 hereafter noticed. 



Respecting their structure, if this term be 

 admissible, it is only necessary to remark that 

 they consist of materials varying from the fine- 

 ness of mud and of sand to the bulk of many 

 cubic feet: and that in their mineral composition 

 they contain fragments of every rock in the sys- 

 tem of nature. Whether the larger fragments 

 are rounded or angular, depends partly on the 

 distance whence they have been transported, on 

 the time and degree during which they have been 



