936 REPORT— 1898. 



An exti-emely violent ' Santa Rosa gale' swept up the Plata estuary. Finding by 

 actual measurement that wlien its waters drove against the outflow of the Parana 

 River they tore 17 feet in one day into the high tosca bluff of San Isidro, I carried 

 the definitive location over the hill instead of round the point at river-level. 



The Inter-Andean Region. — The eastern inland Cordillera of the Andes which 

 overlooks the Gran Chaco is separated from the Pacific coast range by a desert, 

 bare and almost waterless belt df mountainous lands, from 250 to 300 miles wide, 

 through the heart of which I have ridden. An e.xtraordinary parallelism exists 

 between the numerous lines of .sierras, mostly running north and south, which fill 

 the space. Between them are deep, scooped-out depressions, sometimes containing 

 salt lagoons. In the rare occasions of violent storms, these receive torrential 

 streams from channels which ordinarily carry but little watei', and many of which 

 are dry for most of the year. The whole district appears to be a southern prolonga- 

 tion of the Titicaca Basin, and possibly may have been so before the Andes reached 

 their present elevation. As it extends southward it grows lower and less broken, 

 and the salinas occupy a larger area until, to the west and north-west of the Sierra 

 de Cordova, they are of enormous extent ; but as latitude 30° is passed the eastern 

 slope of the now narrow Andean chain begins to receive a sufficiently increased 

 rainfall to supply the waters for the western system of Argentine rivers which try 

 to find their way southward to the river Colorado, but which they only reach at 

 rare intervals, when some exceptionally heavy storm aids their efibrt to satiate the 

 sandy, thirsty desert which they traverse. This area of about 2-50,000 square miles 

 (not a very comfortable country to march an army across) frequently presents 

 evidences of marine action on a grand scale. D'Orbigny, Darwin, De Moussy, and 

 Burmeister allude to the accumulations of rolled shingle found in the valleys and 

 at the base of the mountains. Darwin speaks of the ocean as having ' long acted 

 at the foot of the eastern Cordillera at nearly the same level as on the basin plains 

 of Chile, and that the origin and transportal of these vast beds of pebbles is an 

 interesting problem.' Perhaps a thorough study may show that the Patagonian 

 gravel beds — 76,000 square miles in area and 50 feet average thickness — were, like 

 the Pampean deposits, in great part derived from the north. For reasons which I 

 shall explain, I believe that all of this terribly eroded, inter- Andean district once 

 had an abundant rainfall, and that, after the heavy material from the mountains 

 had been sorted out, the rivers carried to the plains, to the west of the present 

 province of Buenos Ayres, immense quantities of sand and clay derived from the 

 masses of gneiss, schists, sandstone, and calcareous rock through which they 

 flowed. For this reason, to the west of the curved boundary line of the Pampean 

 beds, between the Ventana and Cordova sierras, the lands are dry, sandy, and 

 uninviting. 



The contour lines of the country around the Lower Colorado appear to indi- 

 cate that this river once emptied into a broad, shallow estuary, which penetrated 

 inland from the present coast line about 116 miles. Over its bottom the 

 Colorado dropped its silt, similar to the Pampean mud, but more siliceous. On 

 what was once its northern shore, it is not surprising that Darwin should find 

 ' an accumulation of high sand dunes, ranging westward from the coast twenty 

 miles distant,' and which he believed ' were formed on the shores of an estuary.' 

 It probably included the present Bahia Blanca and its coast line as far as Moimt 

 Ilermoso, to the east of Punta Alta, where Darwin found so many fossil remains 

 of gigantic mammifers. May we not suppose that these came from the north, were 

 floated down the Colorado, and taken to tnis point by the northern currents which 

 sweep along the Patagonian coast ? 



Climatic Ivjluences. — It must be admitted that an ancient sea two-thirds the 

 size of the Mediterranean, and a lake much larger than the total area of the 

 ' Great Lakes ' of North America, must have profoundly affected the climatic con- 

 ditions of the adjoining regions. Perhaps no part of the world presented an 

 example where the forces of Nature had an opportunity to display their power in 

 equal magnitude, over such a continuous area, and with such ixninterrupted 

 simplicity. To the west, the Andes served as a lofty condenser, which, for a dis- 

 tance of over 2,500 miles, guided the cold polar currents towards the equator and 



