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. It? 
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 n 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 
