Chap. II. OTHEALTHINESS OF BRANCH RIVERS. 95 



doubt, that gold is occasionally found within two or 

 three days' journey of Aveyros ; but all lengthened 

 search is made impossible by the scarcity of food and 

 the impatience of the Indians, who see no value in the 

 precious metal, and abhor the tediousness of the gold- 

 searcher's occupation. It is impossible to do without 

 them, as they are required to paddle the canoes. 



The weather, during the month of July, was uninter- 

 ruptedly fine ; not a drop of rain fell, and the river sank 

 rapidly. The mornings, for two hours after sunrise, 

 were very cold ; we were glad to wrap ourselves in 

 blankets on turning out of our hammocks, and walk 

 about at a quick pace in the ea^ly sunshine. But in the 

 afternoons the heat was sickening ; for the glowing sun 

 then shone full on the front of the row of whitewashed 

 houses, and there was seldom any wind to moderate 

 its effects. I began now to understand why the branch 

 rivers of the Amazons were so unhealthy, whilst the 

 main stream was pretty nearly free from diseases aris- 

 ing from malaria. The cause lies, without doubt, in the 

 slack currents of the tributaries in the dry season, and 

 the absence of the cooling Amazonian trade-wind, which 

 purifies the air along the banks of the main river. The 

 trade-wind does not deviate from its nearly straight 

 westerly course, so that the branch streams, which run 

 generally at right angles to the Amazons, and have a 

 slack current for a long distance from their mouths, are 

 left to the horrors of nearly stagnant air and water. 



Aveyros may be called the head-quarters of the 

 fire-ant, which might be fittingly termed the scourge 

 of this fine river. The Tapajos is nearly free from 



