274 Dr. Mac Culloch on the 
criminate. Occasional marks of transportation might easily 
be overlooked over an enormous space, where 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. But 
geologists accustomed to investigation, are sufficiently aware 
of the ease with which errors of this kind are committed (par- 
ticularly where no theory is present to point out what, appear- 
ing trifling, is truly essential) to feel no surprise at oversights 
of this nature, even in such a geologist as Brocchi. 
That I may not, however, prolong this examination too far, I 
shall merely suggest two circumstances more, which may easily 
prove sources of errorin reasoning about these Italian alluvia.. It 
is far from certain, that the two beds can every where be distin- 
guished, merely by their natures, exclusively of the remains 
which they contain. A sandy stratum must 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. This is sufficiently obvious. It is also matter of noto- 
riety, that volcanic eruptions and earthquakes have produced 
great confusion, even in recent times, in many parts of the 
surface of Italy; and when we consider the great number of 
ancient volcanoes in that country, sixty craters remaining in a 
very small tract, we need be at no loss in assigning abundant 
causes for disturbances and anomalies in the appearances of 
the superficial strata. 
It is detracting nothing, therefore, from the merits of the 
Italian geologist to criticise his remarks; nor are his facts per- 
verted, when they are thus rectified on acknowledged and 
obvious principles. The view here entertained of their real 
bearings is indeed amply confirmed by the great majority of 
the facts that are stated in his works; by which the distinction 
of two strata, one containing marine and the other terrestrial 
remains, is proved, even by himself. There is little doubt that 
