THE SANTA CRUZIAN REGION. 



217 



the region near the coast, between the Gallegos and Coy Rivers, they en- 

 tirely replace the rolling prairie lands that prevail to the south and about 

 the headwaters of these streams. About the mouth of the Gallegos River, 

 along the lower course of the Rio Chico, and between the latter stream 

 and the Magellan Strait there are numerous remains of extinct volcanoes. 

 These have given origin to local lava beds, usually, however, of quite 

 limited extent. Some of these ancient craters, like the Friars {Los 

 Frailes), a few miles south of the mouth of the Rio Chico, rise to such a 

 height above the surface of the surrounding country as to almost deserve 

 the distinction of being referred to as mountains. Along the western 

 border, for a distance of from twenty to thirty miles eastward from the 

 base of the mountains, the surface of the plains is covered with a thick 

 deposit of glacial materials left by receding glaciers. These now appear 

 as narrow ranges of low, rounded hills, interspersed with small glacial 

 lakes, or ponds, and separated by somewhat broader stretches of level and 

 open meadow lands. 



The Santa Cruzian Region. — This embraces all that portion of the 

 Patagonian plains lying north of the fifty-first parallel and within the' lim- 

 its of the part of Patagonia now under discussion. It thus includes all 

 the plains region drained by the Desire, St. Dennis, Chico, Sheuen, and 

 Santa Cruz Rivers. It should be noted in this connection that I have 

 limited this region so as to include only the plains region drained by 

 these rivers, for one of these, the Santa Cruz, although by far the most 

 important, in point of size, of all the rivers of these plains, really drains 

 but a very small proportion of the surface of the latter. It is unique 

 among the rivers, not only of this region, but of all eastern Patagonia, in 

 that, instead of having its source in the foothills of the Andes, or the high 

 plateaus at their base, it enters the very confines of these mountains and 

 takes its source in Lakes Argentino and Viedma, which lie within the 

 Andean ranges. It thus drains a considerable area of country within 

 the belt of maximum precipitation, which extends all along the moun- 

 tainous region of the west. When, finally, it emerges from the eastern 

 extremity of Lake Argentino into the plains region, it appears as a noble 

 river, and after its appearance on the plains the volume of its waters is 

 increased by only one or two very insignificant tributaries. 



The climate of the Santa Cruzian region is far more arid than that of 

 the Magellanian, while the rolling prairies of the latter are replaced by 



