100 THE AMERICAN JOURNAL OF SOCIOLOGY
were also factors of isolation. In Europe they were incon- siderable in comparison with those of Asia and America; the Brahmaputra and Ganges in India, the Hoang-Ho and the Yang- Tse-Kiang in China, the Paraguay, Amazon, and Parana in South America, and the Mississippi in North America were, for a long time, and still are, hostile elements to the extension of social relations, although, like all others, they may have been able to favor the earlier settlements.
The prehistoric civilizations on small rivers seem to have pre- ceded those on the large rivers and lakes, then came those of the inland seas; finally, when civilization became world-wide, the large oceanic social structures appeared, those on the inter- continental seas, and in this sense equally inland. Today the most important cities, notably almost all the capitals, are on rivers or on seas having a direct or indirect outlet to the oceans. The oceans, formerly natural barriers, have been transformed into organs of co-ordination of all civilizations of things, ideas, and men. Thus the foundations of a unified social structure have been constituted, and the different stages of which, limited less and less narrowly by conditions at the same time constant and variable, but whose continued development, although world-wide, is none the less limited in time as well as in space by the extent and permanence of the planet.
The civilizations in the deltas of the large rivers, such as the Egyptian, Assyrian, and Chinese, and later that of Italy, Gaul, and Germany, required a large collective development, in extent, duration, and intensity; they necessitated, in fact, the enormous work of generations, collective, simultaneous, and successive, such as canals, embankments, roads, etc. But let us note the difference : formerly this work was performed by slaves or by conquered peoples ; now, as for example, in Holland there is a veritable little republic, with or without central administration, which administers and directs all the work relative to the main- tenance of embankments. In a part of Belgium and Holland this requires constant work and a natural community of effort, surveillance, and direction. Thus each polder forms a sort of civil person (wateringue)', it is administered by a council elected
