PHYSICAL HISTORY OF THE AMAZONS. 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 

 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 Amazon^,'' will 

 give an idea of their aspect. 



