ON THE ALLUVIAL DEPOSITS. 



amber, supposed to belong to alluvial soils, appertain 

 to the marine deposits, these considerations may often 

 explain their present positions, as their beds will be 

 the very alluvia in question. 



Alluvia of unknown Origin. 



The next of the antient alluvia are the inferior of 

 the terrestrial ones, and they may also be considered 

 as of a general nature, to distinguish them from those 

 which are the produce of visible actions. Of the pro- 

 bable causes of antient currents I have treated, in the 

 twenty-second chapter ; and that such currents did 

 attend the elevations of the strata, seems fully proved 

 by the nature and positions of conglomerate rocks. 

 I have shown that the strata of schist and sandstone 

 must have been the produce of slow actions, while 

 the conglomerates were the result of tumultuary ones. 

 These, it is remarkable, occur wherever an entire 

 change of parallelism takes place, or, at those points 

 which mark extensive revolutions of the earth. They 

 were probably formed from the tumultuary alluvia of 

 the waters put into motion by those changes ; and 

 they indicate, by analogy, that similar actions must 

 have produced the corresponding alluvia on our globe, 

 which are as yet unconsolidated. I need not suggest 

 more minutely the explanations which might be of- 

 fered of their various appearances and modifications ; 

 but I have formerly pointed out one cause, in early 

 and peculiar rains, sufficient to produce great effects, 

 and perhaps some of those which cause our present 

 difficulties. That they are often confused by modern 

 actions and modern alluvia, I shall shortly indicate; 

 and hence the frequent, or the almost insuperable dif- 

 ficulty of distinguishing them, with the perpetual 

 mistakes under which the recent ones have been re- 



