Actions of Volcanoes. 273 
from misapprehending the real nature of these appearances. 
When also an opinion of their unintelligible derangement had 
once been adopted, much more confusion than was actually 
present was supposed to exist, where a little attention would 
have solved all the imaginary difficulties. Had Brocchi ori- 
ginally proceeded on a proper theory, there is little doubt that 
he would have found every thing easy, and have rendered it 
equally so to his readers. 
According to this author, similar shells are sometimes found 
in both the alluvial beds ; but it is moreover stated in a general 
way, that the more conspicuous marine remains occur in both. 
Yet, at the same time, it is said, and in a much more decided 
manner, that these are far more numerous in the marl bed 
than in the arenaceous one, and that the shells occur in colonies, 
just as they lived in the sea. It is also remarked, that the 
marine remains bear no marks of transportation ; and further, 
that the terrestrial ones are generally found a few feet only be~ 
neath the surface, and in the upper bed; although, when that 
is absent, they occur in the lower. As that which I have un- 
dertaken to prove is, that the lower, or marl bed, is a marine 
alluvium, and the upper a terrestrial one, it is necessary to try 
to reconcile these anomalies, as well as that which consists in 
the confusion among the volcanic tufas and the alluvial sub- 
stances. 
_ The entire absence of all organic remains requires no expla- 
nation. Where the terrestrial alluvia are wanting, the organic 
substances that would otherwise be found in them, must neces- 
sarily appear to lie in the marine or lower stratum, however 
slightly covered or truly superficial they may be. Though, 
found somewhat deeper, it is 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 distin- 
guish appearances, which, even then, are often difficult to dis- 
Vox. XIV. oY 
