960 PROFESSOR J. PRESTWICH ON THE EVIDENCES OF A SUBMERGENCE 
the waters rose, the area of this plain became more and more circumscribed (fig. 21), 
and retreat more and more impossible, except through a few rare passes in the range 
of hills, until, at last, the animals were driven together at the base of the hills, 
where they, were stopped by mural precipices impassable to the larger and heavier 
animals, though some of the more active and agile Ruminants and Carnivores may 
have, and, judging by the rarity of their remains, probably did escape to the 
Fig. 21 ,—The Tlain of Palermo with its Amphitheatre of Hills. 
Ml Ossiferous breccia. X Caves. 
1. Pliocene strata (witli a narrow belt of Eocene beds in places). 
2. Cretaceous and Jurassic strata. 
The boundary line between 1 and 2 gives approximately a contour line of from 150 to 200 feet above 
sea-level. The slope thence to the sea is very gradual. Above the Pliocene plain, rocks of Hippurite 
limestone rise abruptly, forming steep cliffs and mural precipices, with breaks in the direction of 
Monreale and in the course of the River Oreto. The dotted lines are supposed to represent roughly the 
portions of the plain gradually occupied by the advance of the sea. These are merely for illustration 
and are ideal, but the boundary lines and heights, given in feet, are taken from the Geological Survey 
Map of Sicily. 
