WANDERING OF THE RIVER 249 



Below Diamante the river leaves the cliff on the 

 left bank and slants across the alluvial plain to the 

 clift on the right bank, which it reaches at San 

 Lorenzo. Over the whole of its thirty miles width it 

 resumes the freedom and regularity of features which 

 it had above La Paz. A comparison of the successive 

 maps of the river shows that the scheme of its move- 

 ments, which one would be tempted to draw up with 

 a regular migration of the islands and loops down 

 river, would not be accurate. The changes of the 

 bed of the river are essentially due to variations in 

 the volume of the different arms, which are constantly 

 changing their size and adapting their shape to the 

 body of water that flows in them. The radius of the 

 curve of each arm is proportional to its volume. A 

 long island is formed between two arms of equal size 

 which both describe symmetrical curves. If the 

 volume of one of them is reduced, its original curve 

 is replaced by sinuosities of smaller radius, and these 

 nibble the edges of the island and give it an irregular 

 shape. If the volume increases again, the winding 

 bed is abandoned and becomes a dead bed, and a 

 larger meander begins. The track followed by the 

 ships then breaks up into a series of meanders over 

 a course of about eight miles and a half, and this 

 means the concentration in a single channel of the 

 greater part of the water of the river, and in narrower 

 bends in the sections where the current is divided 

 between several arms. 



From San Lorenzo to San Pedro the river flows by 

 the cliff of the right bank. It is remarkably regular, 

 and has only one slight bend : an exceptionally good 

 site, on which the town of Rosario is built. At almost 

 equal intervals, differing by only about ten to thirteen 

 miles, the river leaves the cliff, and is separated from 



the San Javier arm, on which many colonies arose. Further north 

 the Parang Mini has been used since 1890 for exporting quebracho 

 timber. 



