238 PATAGONIAN EXPEDITIONS: GEOGRAPHY. 



few streams of this region are so completely dammed and choked with 

 glacial detritus that, instead of flowing streams, they present a series of 

 small lakes and marshes which extend interruptedly for a distance of 

 some sixty miles from the base of the Andes. Here, as deep, dry and 

 desert caiions, they enter the basalt region to the eastward, from which 

 they emerge in an equally desiccated condition and continue to the coast 

 as broad, deep, but open valleys, with only a few springs and saline lakes 

 scattered along their bottoms, where, in the remote past, there rolled 

 mighty rivers. Such is the condition of the present valleys of the de Bajo, 

 St. Dennis and Desire Rivers. 



The Rio Chico of the Gallegos. — This is the southernmost of the rivers 

 of the Patagonian plains. It has its source in the rather high pampas 

 east of Laguna Blanca and, with few tributaries, it runs in a northeasterly 

 direction through a not very deep, but broad valley, and empties into the 

 Gallegos some five miles above the mouth of that river. Its drainage 

 basin is small, and, though lying well within the Magellanian region, 

 where the annual precipitation even over the plains is considerable, its 

 water supply is precarious, especially during the autumn and late sum- 

 mer months, since none of its tributaries extend back into the Andes 

 within the limits of perpetual snow. It falls among those rivers which 

 have been classed as intermittent, for, while during the spring and early 

 summer months, when the snows are melting on the higher pampas, it 

 sends a considerable volume of water direct to the sea, its normal condi- 

 tion is that of a small river with a rapid and continuous flow near its 

 source, gradually becoming more sluggish until, in its middle course, it is a 

 deep, narrow, quiet stream with low banks, the surface of its waters but little 

 below that of the surrounding valley, as it meanders back and forth from 

 one side to another through the swamps that in this region cover the sur- 

 face of the latter. These conditions continue until within a few miles 

 of its mouth, when its waters become completely absorbed by the accum- 

 ulations of silt and underlying shingle and its lower channel is here entirely 

 desiccated, save for a few small springs. 



The Gallegos River. — This, the most important of the rivers south of 

 the Santa Cruz, discharges into the Atlantic at Cape Fairweather, in 

 latitude 51° 30' south. For the lower twenty-five miles of its course it 

 partakes of the nature of a broad inlet from the Atlantic, with a breadth 

 at the village of Gallegos of three miles. It is here affected by the 



