154 PATAGONIA AND SHEEP-REARING 



The sandstone and marl cliffs which enclose it become 

 gradually lower as one goes downward. They dominate 

 the valley at a height of 650 feet at the confluence of the 

 Neuquen, and are only 100 to 130 feet high at Patagones. 

 At the foot of them are broad terraces cut by dissymetri- 

 cal ravines, in which the beds of sandstone outcrop on 

 the western slope, exposed to the winds, while the eastern 

 slopes are covered with gravel. On the banks of the 

 river there is a strip about two miles wide with abundant 

 herbaceous vegetation between lines of willows. 

 This is covered by the normal floods. The remainder 

 of the river plain, to the foot of the cliffs, has only a 

 thin scrub, with dunes at intervals. Saline clays here 

 overlie the river gravels. The level of the under- 

 ground water, which is fed by the river, sinks lower 

 as one goes from the banks toward the cliffs. Few 

 parts of the tableland have so desolate an aspect as 

 the bottom of these great Patagonian valleys, when they 

 have not been transformed by irrigation. The pastur- 

 age is poor. At Conesa, however, the valley (costa) 

 is used as summer pasture when there is a shortage 

 of water on the surrounding tableland (planeza). 



The water-supply is good, the volume of the river 

 ranging from 200 to 900 cubic metres a second. Low 

 water lasts from February to April (end of the summer). 

 From May to July the river has sudden and violent 

 floods an effect of the autumn rains. The curve 

 sinks again in August and September, to rise once 

 more in October and December, when the snow melts 

 on the Andes. The Limay, the upper basin of which 

 contains large, lacustrine sheets, is more regular than 

 the Neuquen, which has very pronounced low- water, 

 as well as dangerous floods in the autumn. The first 

 attempts at irrigation date from 1885, when the canal 

 of the Roca colony was dug. Others were made lower 

 down at a later date. The co-operative groups organized 

 for the administration of the canals have not been quite 

 as successful as might have been expected. The 



