26 
KIRTLEY F. MATHER 
season the stream had straightened its course and abandoned a 
long-used channel; elsewhere the river banks were reduced to a 
knife-edge by the close crowding of meander loops. 
Apparently there is a definite correlation between the meander 
pattern and the volume of the stream; this conclusion is really 
the excuse for this brief note. Where the river volume is com- 
paratively small, meander curves are numerous, close-crowded, 
and short. With increase in volume the curves become longer, 
more widely spaced, and fewer. Three distinctive patterns are 
clearly shown in figure 2. These correspond to the varied 
volume of the streams involved. The Secure above its junction 
with the Isiboro displays twice as many meander curves in a 
given distance as are found below Puerto Calvimonte, where its 
volume is nearly doubled by the accession of the Isiboro. Like- 
wise the lower part of the Secure has many more meanders than 
has the Mamore, much the larger of the two streams. 
This change in meander pattern seems to be solely a response 
to the change in volume of the rivers. The gradient is not 
altered, nor is the current appreciably swifter. The change, as 
indicated by the map, involves a lengthening of the straight 
stretches between the short sharp curves. Possibly the greater 
inertia incident upon the larger volume is the major cause of the 
modification. 
It is of interest to note that in this land, where transportation 
routes and lines of travel are restricted to the navigable waters, 
the untutored Indians are sufficiently adept physiographers to 
note this correlation between river volume and meander dimen- 
sions. Distances between chacras, the tiny clearings under culti- 
vation along the river banks, are reported in terms of the num- 
bers of “turns” in the river’s course. Thus I was told that it 
would be five ^Turns’’ from the mouth of the Secure to the port 
of Trinidad; biit that because the Alamore was very wide the 
“turns” were very long, and it would require from sunrise to 
sunset to traverse the distance. 
A little later in the same field season I had opportunity to 
check the conclusion, reached on the Secure and Mamore, by 
similar observations on Rio Heath and its tributary, Rio Najegua, 
