PHYSICAL HISTORY OF THE AMAZOXS. 415 
In the neighborhood of Almeyrim, at a short distance 
from the northern bank of the river, and nearly parallel 
with its course, there rises a line of low hills, interrupted 
here and there, but extending in evident connection from 
Almeyrim through the region of Monte Alegre to the heights 
of Obydos. These hills have attracted the attention of 
travellers, not only from their height, which appears greater 
than it is, because they rise abruptly from an extensive plain, 
but also on account of their curious form ; many of them 
being perfectly level on top, like smooth tables, and very ab- 
ruptly divided from each other by low, intervening spaces.* 
Nothing has hitherto been known of the geological structure 
of these hills, but they have been usually represented as 
the southernmost spurs of the table-land of Guiana. On 
ascending the river, I felt the greatest curiosity 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 con- 
tent myself with examining the structure of the valley so 
far as it could be seen on the river-banks and in the neigh- 
borhood 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 
D A 
region being higher than elsewhere. As I was detained by 
* The atlas in Martins's "Journey to Brazil," or the sketch accompanying 
Bates's description of these hills in his "Naturalist on the Amazons,' will 
give an idea of their aspect. 
