306 C. W. HAYES GEOLOGY OE NICARAGUA CANAL KOUTE 



The eastern division, in which the rain is distributed with tolerable 

 uniformity throughout the year, is covered with a dense tropical forest. 

 The only breaks in this forest are the stream channels and the open 

 lagoons, or those so recently silted up that the soil is not sufficiently 

 firm to support large trees. Throughout this region there are no human 

 habitations, except in the few small towns along the coast and an occa- 

 sional hut in a clearing on the banks of the rivers. There are no roads 

 or other means of intercourse except by way of the streams. 



The most directly apparent effect of the forest is to protect the land 

 surface from erosion. The falling rain is intercepted by the canopy of 

 foliage, and filters down gradually to the surface, where the smaller vege- 

 tation consists largely of i)alms, whose broad leaves afford a still further 

 ])rotection, so that the soil never receives the direct impact of the rain- 

 drops. Since there are no forest fires, the surface is more or less perfectly 

 covered with forest litter, which acts as a further protective covering to 

 the soil. 



The character of the soil will be described more fully in treating of the 

 regolith, but it may be stated here that the surface of this eastern divis- 

 ion, wherever it rises above the level floodplains of the streams, is com- 

 posed of a tenacious red clay. This clay never becomes dry enough to 

 be intersected by shrinkage cracks, and is, of course, never loosened b}'' 

 the action of frost. Although it is penetrated by roots and to some ex- 

 tent by the burrows of insects, it nevertheless resists degradation to a 

 remarkable degree. It was often observed that during a heavy rainfall 

 the water flowing from the steep hillsides would be scarcely at all dis- 

 colored by sediment. 



After a careful study of the region it was concluded that the absence 

 of frost more than counterbalances the enormous rainfall, and that deg- 

 radation of the surface is, on the whole, slower than in temperate regions, 

 where the rainfall is less than a quarter of that in Nicaragua, but where 

 the surface soil is thoroughly loosened by the action of frost. 



Many of the small brooks which carr}^ water throughout the year and 

 have very steep gradient flow in shallow channels cut in this clay. • The 

 clay often forms cascades, and appears to offer more resistance to corra- 

 sion than many varieties of rock. Although the hill slopes are steep, 

 they are comparatively smooth, not deepl}^ gullied, as is usualh^ the case 

 in temperate regions, and it is onl}^ after the water has collected in con- 

 siderable volume that it is able to lower its channel through the clay to 

 the underlying rock. 



A further effect of the vegetation, and hence indirectly of the climate, 

 is that many of the streams are filled with an abundant growth of vege- 



