80 A JOURNEY IN BRAZIL. 
geology, and the almost universal decomposition of the 
rock surfaces, making it difficult to decipher them. The 
presence of the drift phenomena, so universal in the North- 
ern hemisphere, has been denied here ; but, in his long 
walk to-day, Mr. Agassiz has had an opportunity of ob- 
serving a great number of erratic boulders, having no 
connection with the rocks in place, and also a sheet of 
drift studded with boulders and resting above the partially 
stratified metamorphic rock in immediate contact with it. 
I introduce here a letter written by him to his friend, 
Professor Peirce of Harvard University, under the first 
impression of the day's experience, which will best explain 
his view of the subject. 
" May 27th, 1865, TIJUCA. 
" MY DEAR PEIRCE : 
"Yesterday was one of the happiest days of my life, and 
I want to share it with you. Here I am at Tijuca, a clus- 
ter of hills, about eighteen hundred feet high and some 
seven or eight miles from Rio, in a charming cottage-like 
hotel, from the terrace of which you see a drift hill with 
innumerable erratic boulders, as characteristic as any I 
have ever seen in New England. I had before seen sundry 
unmistakable traces of drift, but there was everywhere con- 
nected with the drift itself such an amount of decomposed 
rocks of various kinds, that, though I could see the drift and 
distinguish it from the decomposed primary rocks in place, 
on account of my familiarity with that kind of deposits, yet 
I could probably never have satisfied anybody else that there 
is here an equivalent of the Northern drift, had I not found 
yesterday, near Bennett's hotel at Tijuca, the most palpable 
superposition of drift and decomposed rocks, with a distinct 
line of demarcation between the two, of which I shall secure 
