VOYAGE FROM NEW YORK TO RIO DE JANEIRO. 15 



In the evening, which is always the most enjoyable part 

 of our day, we sat on the guards and watched the first tropi- 

 cal sunset we had yet seen. The sun went down in purple 

 and gold, and, after its departure, sent back a glow that 

 crimsoned the clouds almost to the zenith, dying off to 

 paler rose tints on the edges, while heavy masses of gray 

 vapor, just beginning to be silvered by the moon, swept 

 up from the south. 



April 1th. To-day the lecture was upon the physical 

 features of South America, something with reference to 

 the geological and geographical work in which Mr. Agassiz 

 hopes to have efficient aid from his younger assistants. 

 So much of the lecture consisted of explanations given 

 upon geological maps that it is difficult to record it. Its 

 principal object, however, was to show in what direction 

 they should work in order to give greater precision to the 

 general information already secured respecting the forma- 

 tion of the continent. " The basin of the Amazons, for 

 instance, is a level plain. The whole of it is covered 

 with loose materials. We must watch carefully the char 

 acter of these loose materials, and try to track them to 

 their origin. As there are very characteristic rocks in 

 various parts of this plain, we shall have a clew to the 

 nature of at least some portion of these materials. My 

 own previous studies have given me a special interest in 

 certain questions connected with these facts. What power 

 has ground up these loose materials ? Are they the result 

 of disintegration of the rock by ordinary atmospheric 

 agents, or are they caused by the action of water, or by 

 that of glaciers ? Was there ever a time when large masses 

 of ice descended far lower than the present snow line of 

 the Andes, and, moving over the low lands, ground these 



