Page:Popular Science Monthly Volume 17.djvu/727

Rh rising. Dr. W. Weiss read a paper before the Berlin Geographical Society at a recent meeting, in which he advanced the theory, founded on a comparison of observations which had been made at the mouths of rivers, that the continent is rising. The Isthmus of Panama seems to be rising, and signs of elevation are apparent on the north coast of the continent. The delta of the Magdalena River has suffered notable changes within comparatively recent times. The tertiary highland of Turbaco, which extends from Carthagena to Sabanilla, was once an island in front of the stream, as is indicated by the forking of the river. One arm of the river empties toward the west near Carthagena, the other arm forms the present mouth with its branches in the lagoon of Santa Marta; ships formerly sailed into the western arm, which is not now navigable. The closing of this branch is generally ascribed to the luxuriant vegetation, but it is more than probable that other causes were combined with it. A small elevation would be enough to stop the flow of water, and the fact that such an elevation has taken place is shown by the discovery of recent shell-beds in a part of the lagoon. The bay of Santa Marta, with its monotonous sand-flats between steep, bald cliffs and island-like uprising knobs, produces the impression of a recently dried sea-bottom. Similar appearances are presented farther east, to such an extent that it was believed in the sixteenth century that the sea had retreated. The region of the lagoon of Maracaybo, and indeed the whole coast of Venezuela, appears to have taken part in a movement of uprising. The existence of the delta of the Orinoco favors the theory of elevation, for, though it can not be held that deltas are not formed except where the ground is rising, it is nevertheless true that elevation is most favorable to their formation. The observations along the coast of the British, French, and Dutch possessions are contradictory; but as a whole they seem to indicate that the land is gaining on the sea. The character of the changes that are taking place at the mouth of the Amazon is generally supposed to indicate a sinking of the land, but there are circumstances that favor the opposite view. The signs that the upper part of the bed of the river is rising are numerous, and all the phenomena of washing away at the mouth which are generally considered evidences of a depression can be accounted for by supposing that the interior is rising faster than the coast. Indications of a recent elevation may be seen all along the coast from Cape St. Roque to the La Plata, in the hardened shore-ridges of the Rio Grande do Norte, Parahyba, and Pernambuco, the elevated shore-lines of Rio Vermiglio, Bahia, and Rio Jequitinhonha, the coral reefs of the Abrolhos, the holes of the sea-urchin found above the level of the sea near Cape Frio, the new formations near Rio de Janeiro, the deterioration of the harbors of Santa Catarina, Porto Alegre, and other places. Darwin proved by the discovery of recent shell-deposits that the region of the La Plata was rising; since then some facts have been adduced pointing to a sinking, but the La Plata affords relations similar to those which have been referred to in the case of the Amazon. A lake in the Straits of Magellan containing marine animals, but situated at a higher level than that of the sea, is cited by Agassiz in proof that a rise of the land has taken place there. On the west coast signs of a sinking appear in the Chonos Archipelago, but they give way to trustworthy evidences of elevation in southern Chili. These continue to Callao and Lima, where a sinking is suddenly indicated. The land at Callao consists of gravel-beds, which may be considered as river and shore formations. Washings away from beneath, assisted by earthquakes, might readily have caused slight local falls, without making it necessary to invoke a sinking of the land. Not enough is known of the coasts north of Callao to justify a definite expression of opinion.

The Law of Mutual Help.—At the Congress of Russian Naturalists and Physicians, held in January last, Professor K, Kessler delivered an address on the law of mutual help, which he urged was entitled to a place by the side of Darwin's law of the struggle for existence. Having given a brief sketch of the theory of the struggle for existence, Professor Kessler remarked that it did not play the only part in organic development. By the operation of the reproductive instinct, there was developed in the different