78 



RIO NEGRO. 



Aug. 1833. 



whence there was no exit; in a more humid dimate the 

 water flowing from the lake would soon have hollowed a 

 channel in the soft strata^ and thus converted the depression 

 of the soil into an ordinary valley. There is reason to believe 

 that the whole of these great plains have been raised above 

 the level of the sea within a recent geological period. May 

 we not then consider the sahnas as the receptacles of the 

 washings of the sedimentary strata ? On this idea we un- 

 derstand their absence where the land is granitic. It is 

 manifest that these great natural evaporating dishes can only 

 occur where the amount of annual rain is small.* 



To the northward of the Rio Negro^ between it and the 

 inhabited country near Buenos Ayres, the Spaniards have 

 only one small settlement^ recently established at Bahi>a 

 Blanca. The distance in a straight line to the capital is very 

 nearly five hundred British miles. The wandering tribes of 

 horse Indians, which have always occupied the greater part of 

 this country, having of late much harassed the outlying 

 estancias, the government at Buenos Ayres equipped some 

 time since an army under the command of General Rosas 

 for the purpose of exterminating them. The troops were now 

 encamped on the banks of the Colorado ; a river lying about 

 eighty miles to the northward of the Rio Negro. When 

 General Rosas left Buenos Ayres, he struck in a direct line 

 across the unexplored plains : and as the country was thus 

 pretty well cleared of Indians, he left behind him, at wide 



t * Almost every circumstance here mentioned, occurs in the salt lakes 



near the borders of the Caspian. That country, like Patagonia, appears 

 to have been recently elevated above the waters of the sea. Pallas states 

 that the salt lakes occupy shallow depressions in the steppes ; that the 

 mud on the borders in every case is black and fetid ; that beneath the 

 crust of sea salt, sulphate of magnesia occurs, imperfectly crystallized ; 

 that the muddy sand is mixed with lentils of gypsum. We have before 

 stated that these lakes are inhabited by small crustaceous animals ; and 

 flamingoes (Edin. New Philos. Jour., Jan. 1830) likewise frequent 

 them. As these circumstances, apparently so trifling, occur in two dis- 

 tant continents, we may feel sure they are the necessary results of some 

 common cause. — See Pallas' s Travels, 1793 to 1794, p. 129 — 134. 



