The plebs, like the English commons, contained families differing widely in rank and social position, among them those families which, as soon as an artificial barrier broke down, joined with the patricians to form the new older settlement, a nobility which had once been the whole people, was gradually shorn of all exclusive privilege, and driven to share equal rights with a new people which had grown up around it.
Only one barrier remained between them.
It is also included in the Paropamisus, though the latter term embraces more, Caucasus being apparently used only when the alpine barrier is in question.
The Apennines (q.v.), as has been already mentioned, here traverse the whole breadth of Italy, cutting off the peninsula properly so termed from the broader mass of Northern Italy by a continuous barrier of considerable breadth, though of far inferior elevation to that of the Alps The Ligurian Apennines may be considered as taking their rise in the neighborhood of Savona, where a pass of very moderate elevation connects them with the Maritime Alps, of which they are in fact only a continuation.
A snow-capped mountain ridge or an arid desert forms a barrier between different forms of life which is often more effective than an equal breadth of sea.
The shores of the larger islands are fringed in some parts with a dense barrier of mangroves, backed by an often impenetrable thicket of tropical undergrowth, which, as the ridges are ascended, give place to taller trees and deep green bushes which are covered with orchids and trailing moss (orchilla), and from which creepers hang down interlacing the vegetation.
Different species of organisms come to perfection in different climates; and it may be stated as a general rule that a species, whether of plant or animal, once established at one point, would spread over the whole zone of the climate congenial to it unless some barrier were interposed to its progress.
It is supplied by the tidaland wind-formed currents, which are drifting sand from the Long Island and New Jersey coasts, extending the barrier beaches, such as Sandy Hook, out across the entrance to New York Bay.
The one known as the Bottomless Pit was for many years a barrier to all further exploration, but it is now crossed by a wooden bridge.
This second barrier is one of the most mighty upheavals in the world, by reason both of its extent and its altitude.