48 Charles Darwin. 



He made his headquarters for his land expedi- 

 tions at El Carmen, about eighteen miles up the 

 river, a town built on the face of a high cliff, some of 

 the houses or homes of the natives being excavated 

 in its face. One of the first objects of interest to at- 

 tract his attention was a famous salt lake. During 

 the rainy season it was a basin of the strongest brine, 

 but when the dry time came, and the hot summer 

 sun poured down, the water evaporated, leaving a 

 pure white patch of gleaming salt, in remarkable 

 contrast to the surrounding verdure. 



This lake was found to be two miles in length, 

 with a layer of salt ranging in thickness from several 

 inches at the border to as many feet in the centre. 

 The interest of the explorer naturally centred in 

 the life of the lake, and he was repaid by the discov- 

 ery of a worm that existed in sufficient quantities to 

 attract flamingoes here to feed. " Well may we 

 affirm," writes Darwin in his log-book, " that every 

 part of the world is habitable ! Whether lakes of 

 brine, or those subterranean 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." 



During a trip to the Colorado River with a band 

 of Gauchos Darwin came upon the sacred tree, about 

 which so much has been said and written, it having 

 been described as taking up foreign objects upon its 

 branches. The tree is a low thorny variety, not com- 

 mon, yet conspicuous on the plains by its peculiar 

 appearance. As the party approached, the tree was 



