78 CHARLES DARWIN 



salt? Flamingoes in considerable numbers inhabit this lake, 

 and breed here; throughout Patagonia, in Northern Chile, 

 and at the Galapagos Islands, I met with these birds wher- 

 ever there were lakes of brine. I saw them here wading 

 about in search of food probably for the worms which bur- 

 row in the mud ; and these latter probably feed on infusoria or 

 confervae. Thus we have a little living world within itself, 

 adapted to these inland lakes of brine. A minute crustaceous 

 animal (Cancer salinus) is said* to live in countless numbers 

 in the brine-pans at Lymington: but only in those in which 

 the fluid has attained, from evaporation, considerable 

 strength namely, about a quarter of a pound of salt to a 

 pint of water. Well may we affirm that every part of the 

 world is habitable ! Whether lakes of brine, or those sub- 

 terranean ones hidden beneath volcanic mountains warm 

 mineral springs the wide expanse and depths of the ocean 

 the upper regions of the atmosphere, and even the surface 

 of perpetual snow all support organic beings. 



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 Bahia 

 Blanca. The distance in a straight line to Buenos Ayres 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 northward of the Rio Negro. 

 When General Rosas left Buenos Ayres he struck in a direct 



* Linnacan Trans., vol. xi. p. 205. It is remarkable how all the circum- 

 stances connected with the salt-lakes in Siberia and Patagonia are similar. 

 Siberia, like Patagonia, appears to have been recently elevated above the 

 waters of the sea. In both countries the salt-lakes occupy shallow depres- 

 sions in the plains; in both the mud on the borders is black and fetid; 

 beneath the crust of common salt, sulphate of soda or of magnesia occurs, 

 imperfectly crystallized; and in both, the muddy sand is mixed with lentils 

 of gypsum. The Siberian salt-lakes are inhabited by small crustaceous ani- 

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

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

 continents, we may feel sure that they are the necessary results of common 

 ', causes. See Pallas' 's Travels, 1793 to 1794, pp. 129-134. 



