544 
ELEMENTS OF GEOLOGY. 
the tropical character of the flora of Monte Bolca and its dis¬ 
tinctness from the sub-tropical flora of the Lower Miocene of 
Switzerland and Italy, in which last there is a far more con¬ 
siderable mixture of forms of a temperate climate, such as 
the willow, poplar, birch, elm, and others. That scarcely 
any one of the Monte Bolca fish should have been found in 
any other locality in Europe, is a striking illustration of the 
extreme imperfection of the palaeontological record. We 
are in the habit of imagining that our insight into the geolo¬ 
gy of the Eocene period is more than usually perfect, and we 
are certainly acquainted with an almost unbroken succession 
of assemblages of shells passing one into the other from the 
era of the Thanet sands to that of the Bembridge beds or 
Paris gypsum. The general dearth, therefore, of fish in the 
different members of the Eocene series. Upper, Middle, and 
Lower, might induce a hasty reasoner to conclude that there 
was a poverty of ichthyic forms during this period; but 
when a local accident, like the volcanic eruptions of Monte 
Bolca, occurs, proofs are suddenly revealed to us of the rich¬ 
ness and variety of this great class of vertebrata in the 
Eocene sea. The number of genera of Monte Bolca fish is, 
according to Agassiz, no less than seventy-five, twenty of 
them peculiar to that locality, and only eight common to the 
antecedent Cretaceous period. 'No less than forty-seven out 
of the seventy-five genera make their appearance for the first 
time in the Monte Bolca rocks, none of them having been 
met with as yet in the antecedent formations. They form 
a great contrast to the fish of the secondary strata, as, 
with the exception of the Placoids, they are all Teleos- 
teans, only one genus, Pycnodus^ belonging to the order of 
Ganoids, which form, as before stated, the vast majority of 
the ichthyolites entombed in the secondary or Mesozoic 
rocks. 
Cretaceous Period. —M. Virlet, in his account of the geolo¬ 
gy of the Morea, p. 205, has clearly shown that certain traps 
ill Greece are of Cretaceous date ; as those, for example, which 
alternate conformably with cretaceous limestone and green¬ 
sand between Kastri and Damala, in the Morea. They con¬ 
sist in great part of diallage rocks and serpentine, and of an 
amygdaloid with calcareous kernels, and a base of serpen¬ 
tine. In certain parts of the Morea, the age of these volcanic 
rocks is established by the following proofs: first, the litho¬ 
graphic limestones of the Cretaceous era are cut through by 
trap, and then a conglomerate occurs, at Nauplia and other 
places, containing in its calcareous cement many well-known 
fossils of the chalk and greensand, together with pebbles 
