Sob C. W. HAYES — GEOLOGY OP NICARAGUA CANAL ROUTE 



divide and the hills bordering the Rivas plain. The remnants of this 

 baseleveled valley are found in the upper Tola basin, while the lower 

 portion of that basin is very perfectly reduced to the present baselevel, 

 only the uniforna summits of a few rounded hills suggesting the former 

 existence of a plain at a higher level. 



In the upper Rio Grande basin the Rivas plain can be traced from its 

 typical development at the present Continental divide westward through 

 the increasing degrees of dissection to the summits of a few hills nearly 

 down to the Tola. The inference, therefore, that the remnants of the 

 plain observed in the upper Tola and in the upper Rio Grande valleys 



Figure 1. — Basins of the Rio Grande and Rio Las Lajas. 

 To illustrate recent shifting of Continental divide. 



were originally portions of the same baseleveled plain, is fairly well estab- 

 lished. Accelerated by the lowering of its outlet, the diverted Tola has 

 itself made considerable progress in the conquest of drainage formerly 

 l)elonging to the eastward flowing streams. It has diverted branches 

 both of the Gonzales and Medio, the reversed streams now forming the 

 ('hacalapa and Matinga, and leaving low gaps in the present Continental 

 divide. The Guachipilin, now flowing into the upper Rio Grande, 

 formerly found an outlet eastward to the Medio. 



The latest diversion has evidently been the Guiscoyol, which was per- 

 haps the largest stream in this region flowing eastward. Its source, now 

 forming the headwaters of the Rio Grande, was in the high hills which 

 border the lower Rio Grande valley. The Rio Grande is thus seen to 

 have a composite course, which now makes a nearly complete circuit 

 before reaching the sea. 



