LIFE IN RIO CONTINUED. 89 
to a new geological agency, thus far not discussed in our 
geological theories. It is obvious here (and to-day with 
the pouring rain which keeps me in doors I have satis- 
factory evidence of it) that the warm rains falling upon the 
heated soil must have a very powerful action in accelerating 
the decomposition of rocks. It is like torrents of hot water 
falling for ages in succession upon hot stones. Think of 
the effect, and, instead of wondering at the large amount 
of decomposed rocks which you meet everywhere, you will 
he surprised that there are any rocks left in their primitive 
condition. It is, however, the fact, that all the rocks you 
see are encased, as it were, in a lining of the decomposed 
part of their surface ; they are actually covered with a 
rotten crust of their own substance. 
" Ever truly yours, 
" L. AGASSIZ." 
Among the objects of special interest which we have 
seen here for the first time are the colossal fruits of the 
Sapucaia-tree, a species of Lecythis, belonging to the same 
family as the Brazilian nuts. These fruits, of which there 
are a number of species, vary from the size of an apple to 
that of an ordinary melon ; they resemble an' urn closed 
with a lid, and contain about fifty seeds as large as almonds. 
The woods all over these Tijuca hills are beautiful and 
wonderfully luxuriant ; but I lack names for the various 
trees. We are not yet familiar enough with the aspect 
of the forest to distinguish readily its different forms of 
vegetation ; and it is besides exceedingly difficult here to 
ascertain the common names of plants. The Brazilians do 
not seem to me observant of nature in its details ; at all 
events, I never get a satisfactory answer to the question I 
