86 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 



