Sharp, and the comparison of the species found with those of the nearest continental land, furnish the student of geographical distribution with many valuable and suggestive facts.
In continental countries the laws are even more stringent.
The three great rivers that form the La Plata system - the Paraguay, Parana and Uruguay - have their sources in the highlands of Brazil and flow southward through a great continental depression, two of them forming eastern boundary lines, and one of them, the Parana, flowing across the eastern part of the republic. The northern part of Argentina, therefore, drains eastward from the mountains to these rivers, except where some great inland depression gives rise to a drainage having no outlet to the sea, and except, also, in the " mesopotamia " region, where small streams flow westward into the Parana and eastward into the Uruguay.
The chain of the Frisian Islands marks the outer fringe of the former continental coast-line, and is separated from the mainland by shallows, known as Wadden or Watten, answering to the maria vadosa of the Romans.
The prevailing winds, mild and humid, are west winds from the Atlantic; continental climatic influence makes itself felt in the east wind, which is frequent in winter and in the east of France, while the mistral, a violent wind from the north-west, is characteristic of the Mediterranean region.
