180 
PHYSICAL HISTORY OF THE 
spaces.* Nothing has hitherto been known of 
the geological structure of these hills, but they 
have been usually represented as the southern¬ 
most spurs of the table-land of Guiana. On 
ascending the river, I felt the greatest curi¬ 
osity to examine them; but at the time I was 
deeply engrossed in studying the distribution 
of fishes in the Amazonian waters, and in 
making large ichthyological collections, for 
which it was very important not to miss the 
season of low water, when the fishes are most 
easily obtained. I was, therefore, obliged to 
leave this most interesting geological problem, 
and content myself with examining the struc¬ 
ture of the valley so far as it could be seen on 
the river-banks and in the neighborhood of my 
different collecting stations. On my return, 
however, when my collections were completed, 
I was free to pursue this investigation, in 
which Major Coutinho was as much interested 
as myself. We determined to select Monte 
Alegre as the centre of our exploration, the 
serra in that region being higher than else- 
* Tlie atlas in Martius’s Journey to Brazil, or the sketch 
accompanying Bates’s description of these hills in his Natu¬ 
ralist on the Amazons, will give an idea of their aspect. 
