PLIOCENE STRATA OF ITALY. 
207 
we are surprised at the great thickness, solidity, and height 
above the sea of the rocky masses in which they are en¬ 
tombed, and the vast amount of geographical change which • 
has taken place since their origin. It must be remembered 
that, before they began to emerge, the uppermost strata of 
the whole must have been deposited under water. In order, 
therefore, to form a just conception of their antiquity, we 
must first examine singly the innumerable minute parts of 
which the whole is made up, the successive beds of shells, 
corals, volcanic ashes, conglomerates, and sheets of lava ; and 
we must afterwards contemplate the time required for the 
gradual upheaval of the rocks, and the excavation of the val¬ 
leys. The historical period seems scarcely to form an appre¬ 
ciable unit in this computation, for we find ancient Greek 
temples, like those of Girgenti (Agrigentum), built of the 
modern limestone of which we are speaking, and resting on 
a hill composed of the same; the site having remained to 
ail appearances unaltered since the Greeks first colonized the 
island. 
It follows, from the modern geological date of these rocks, 
that the fauna and fiora of a large part of Sicily are of high¬ 
er antiquity than the country itself. The greater part of 
the island has been raised above the sea since the epoch of 
existing species, and the animals and plants now inhabiting 
it must have migrated from adjacent countries, with whose 
productions the species are now identical. . The average du¬ 
ration of species would seem to be so great that they are 
destined to outlive many important changes in the config¬ 
uration of the earth’s surface, and hence the necessity for 
those innumerable contrivances by which they are enabled 
to extend their range to new lands as they are formed, and 
to escape from those which sink beneath the sea. 
Newer Pliocene Strata of the Upper Val d’Arno. — When 
we ascend the Arno for about ten miles above Florence, we 
arrive at a deep narrow valley called the Upper Val d’Arno, 
which appears once to have been a lake, at a time when the 
valley below Florence was an arm of the sea. The horizon¬ 
tal lacustrine strata of this upper basin are twelve miles long 
and two broad. The depression which they fill has been 
excavated out of Eocene and Cretaceous rocks, which form 
everywhere the sides of the valley in highly inclined strati¬ 
fication. The thickness of the more modern and unconform- 
able beds is about 750 feet, of which the upper 200 feet con¬ 
sist of Newer Pliocene strata, while the lower are Older Pli¬ 
ocene. The newer series are made up of sands and a con¬ 
glomerate called sansino.” Among the imbedded fossil 
