326 C W. HAYES — GEOLOGY OF NICARAGUA CANAL ROUTE 



mantle of vegetation. This consists of a heavy forest growth, except 

 where the land surface has been so recently reclaimed from swamps and 

 lagoons that it has not yet been invaded by the forest, or that its surface 

 is not sufficiently firm to support forest trees. Even where the forest 

 does not extend, the smaller vegetation is extremely dense and the sur- 

 face is even more effectually protected than under the forest. It may 

 be stated in general, however, that all of the land which rises above the 

 margins of the extensive fioodplains and the silt-filled valleys — that is, 

 all which is underlain by rocks older than the recent silt — is forest clad. 

 The canopy of foliage formed by the treetops is so perfect that much of 

 the light and all of the direct sunlight is intercepted; hence the smaller 

 vegetation at the surface is not exceptionally luxuriant and only par- 

 tially covers the surface. 



The forest trees of this region are nearly all deciduous, but the season 

 of shedding their foliage is different for different species ; hence there is 

 a continuous supply of forest litter throughout the entire year, and its 

 decay not being checked by frost is a continuous process. 



All rocks of this eastern division show the effects of weathering to great 

 depth, not only the igneous but the sedimentary rocks as well. In the 

 course of the drilling operations which were carried on in this region a 

 large amount of data was obtained concerning the depth to which decay 

 has gone in rocks of various origin and composition, and also the 

 products of the weathering. 



PROD UCTS OF SOCK DEC A Y 



Classes in general. — The final product of rock decay in this region is a 

 red clay. This represents the complete oxidation of all the constituent 

 minerals of the rock except the quartz, and the complete obliteration of 

 the original rock structure. From this extreme the products of rock de- 

 cay present all possible gradations to the perfectly fresh rock. While 

 there are no sharp lines of demarkation between different phases of the 

 ;.'ock weathering, the products may be conveniently though somewhat 

 arbitrarily separated into three groups, namely, red clay, blue clay, and 

 soft rock. The first two differ chiefly in the degree of oxidation, and 

 the second differs from the third chiefly in the extent to which the orig- 

 inal structure of the rock has been obliterated. The third group itself 

 is not sharply separated from the fresh rock, but passes into it in most 

 cases by imperceptible gradations. 



Red clay. — As already stated, in the eastern division of the region under 

 discussion all portions of the surface which rise above the margins of 

 the alluvial flood plains are covered with red clay — the final product of 

 rock decay. 



