ON THE ELEVATED SUBMARINE ALLUVIA 305 



not difficult to understand how this might happen, as 

 well as how the marine remains may occasionally 

 occur in the upper alluvia. Revolutions of the surface, 

 and principally from partial transportation by rivers, 

 must inevitably have generated much confusion of this 

 kind, capable, even in the hands of a good observer, 

 of misleading him in his conclusions, unless previously 

 on his guard to distinguish appearances which, even 

 then, are often very difficult to discriminate. Oc- 

 casional marks of transportation might easily be over- 

 looked over an enormous space, when the principal 

 facts were of a different nature; as these latter would 

 form a sort of standard for the whole, and would 

 naturally lead to a neglect of such petty variations as 

 seemed to be uninteresting. 



Not to prolong this examination too far, I shall 

 merely suggest two more circumstances which may 

 easily prove sources of error in reasoning about these 

 Italian alluvia. It is far from certain that the two 

 beds can every where be distinguished merely by their 

 natures, exclusively of the remains which they con- 

 tain. A sandy stratum must necessarily in some 

 places have formed the bottom of the sea, as well as 

 a muddy or marly one. Thus the marine alluvium 

 may easily be confounded with the terrestrial one; 

 beds of alluvial matter not admitting of that separation 

 which so generally marks different solid strata, even 

 where the nature of the two beds in contact is the 

 same. It is possible indeed that much of the appa- 

 rently terrestrial alluvium is itself marine; a suspicion 

 which, it will be seen in a future chapter, attaches to 

 many alluvial deposits. It is also notorious that vol- 

 canic eruptions and earthquakes have produced great 

 confusion, even in recent times, in many parts of 

 Italy: and when we consider the great number of 



