RIOS SECURE AND MAMORE, EASTERN BOLIVIA 27 
on the frontier between northern Bolivia and eastern Peru (fig. 1). 
The Najegua is less than a third as large as the Secure, but its 
gradient is approximately the same. In harmony with its slight 
volume, its meander curves were very short, extremely close 
spaced, and numerous. Working upstream in it, at a pace of 2| 
miles per hour, it was necessary to take bearings every minute or 
two in order to get any results at all from the effort to map its 
tortuous course. Rio Heath, only slightly less in volume than the 
Secure, has a meander pattern practically identical with that of 
the Secure above Puerto Calvimonte. 
