The matter is this: Along the north shore of the Caribbean Sea the coasts are deep and rocky, but further south, as the Cordilleras decrease in elevation, the shore is lined with sandbanks, and can be approached only through shallow estuaries, just as the coasts of the Mediterranean become sandy at their southeastern extremity, the only point where the circle of lofty coast ranges is broken by the delta of a swamp river—the depth of the shore waters being apparently proportioned to the height of the shore lands. Even single depressions in the chain of a long-stretched coast range are often confronted by isolated sandbanks—as if a collapse of the mountain walls had shoaled the littoral sea. But at Panama that tendency is aggravated by another cause. For the last two hundred years the line of the overland route has followed the Rio Chagres and its western tributaries; the adjoining hill country became studded with settlements, and, as usual in Spanish colonies, “civilization” led to forest destruction and progressive aridity. The abundant rains of the summer solstice, which were formerly absorbed by the not less exuberant vegetation of a tropical coast region, now reach the valley in the form of raging torrents, saturated with the mould of the treeless hill-slopes; and the alluvium deposited at the river mouth has thus gradually formed silt banks, against which the repeated improvements of the estuary have proved only a temporary remedy. The Russians had a similar experience with the port of Azof, once the best harbor in the basin of the Euxine; but after the destruction of the inland forests the naked hills of the Don revenged themselves by a hydra growth of dunes that defied all expedients of human skill, and after diking and dredging away some ninety million roubles, the government yielded to Nemesis and removed the wharves to the harbor of Taganrog. In order to enable vessels of deeper draught to enter the mouth of the Chagres, the canal itself would have to be supplemented by a _channel mole_, a marine canal of nine miles, protected by dikes which in their turn might become a source of peril to sailing vessels approaching the estuary during the prevalence of the frequent gales which make the headlands of the southern Caribbean so many Guardafuis.