In this conjecture he was at error, for in 1877 Dr. F. Moreno successfully determined the source of the Santa Cruz as being taken from a lake situated in lat. 50° 14′ S., and long. 71° 59′ W., some miles from Lake Viedma, with which, however, it has no visible communication. This fine sheet of water measures thirty miles from east to west, and ten miles at its greatest breadth; its depth Dr. Moreno was unable to ascertain—with a line of 120 feet he could find no bottom at a short distance from the shore.
According to the same authority the greatest depth of the river is seventy feet, but the rapidity of the current, in some places as much as fifteen miles an hour, must have prevented reliable soundings being taken.
Near Lake Viedma is a volcano, the Chalten, which, according to the Indians, still throws out quantities of ashes. At the time Dr. Moreno was there, a column of smoke was issuing from its crater.
The country around Santa Cruz River differs in no way from that I had already traversed, one of the peculiarities of Patagonian landscape being its complete sameness. The plains, which occupy the greater portion of the country, extend along the Atlantic Ocean. The line separating them from the fertile mountain regions is extremely sharply defined. Beginning at Cape Negro, Magellan Straits, lat. 53° S. and long. 75° 50′ W., it runs thence west-north-west to the north-eastern extremity of Otway Water, following the channels of Fitzroy Passage, and the northern shores of Skyring Water to long. 72° W., and then extends along the eastern shores of Obstruction Sound and Kirke Water, running then due northward towards Lake Viedma. These plains rise almost uniformly, 300 feet high, one above another, like terraces, and are traversed occasionally by ravines and flat-bottomed depressions, which latter frequently contain salt lakes. The formation of the country is tertiary, resting on porphyry and quartz, ridges of which often protrude through the surface. Near long. 70° W. the plains are capped with a layer of lava, about a hundred miles in width.
Darwin accounts for the regularity with which the plains rise one over the other by the supposition that the land has been raised in a mass from under the sea, the upheaving movement having been interrupted by at least eight long periods of rest, during which the sea ate deeply back into the land, forming at successive levels the long lines of escarpments which separate the different plains.
In that strange country the vegetable kingdom is as little varied as the aspect of the landscape: from Chubut to Sandy Point, from the sea-coast to the Cordilleras, one meets the same few species of miserable stunted bushes and coarse grasses.
The following is a cut showing the formation of the country at Port St. Julian:*
* From a perforation made by E. de Ville Massot, C.E.