No. 392.] REVIEWS OF RECENT LITERATURE. 679 
GEOLOGY. 
The Physiography and Geology of the Nicaragua Canal Route 
were studied by Dr. C. Willard Hayes, of the United States Geolog- 
ical Survey, during ten months’ field work in 1898, in connection 
with the surveys made by the Nicaragua Canal Commission, of which 
Admiral J. B. Walker is president. The more general results of 
these studies have recently been published in a concise form and 
should be of interest to naturalists as well as to geographers and 
geologists.‘ The summary of the conclusions reached, as published 
by Dr. Hayes atthe close of his admirable paper, is as follows: 
“The region discussed embraces the belt of country extending 
from the Caribbean Sea to the Pacific in northern Costa Rica and 
southern Nicaragua, adjacent to the route of the proposed Nicaragua 
canal. 
“ Its most important physiographic feature is the broad depression 
which extends diagonally across the isthmus, between the recent vol- 
canic ranges on the southwest and the Chontales hills on the north- 
east. The topography of this depression is chiefly that of an old 
land, generally reduced to the condition of a peneplain by streams 
flowing in opposite directions from a former divide near the axis of 
the isthmus. 
“The rainfall on the Caribbean side of the isthmus is very abun- 
dant and distributed uniformly throughout the year. On the Pacific 
side it is less abundant and confined to half the year. This climatic 
difference produces striking differences in vegetation, rock decay, 
rate of erosion, and resulting topographic forms. 
“The rocks of the region are largely volcanic products, with two 
sedimentary formations of Tertiary (Oligocene) age, and no rocks 
occur which are certainly older than the Tertiary. The igneous rocks 
are in part contemporaneous with the Tertiary sedimentary formations 
and in part recent. 
“On the east side high temperature with abundant moisture and 
consequent rank and rapidly decaying vegetation afford exceptionally 
favorable conditions for rock decay, which has extended to great 
depths and yields red clay as the final product. On the west side 
alternate wet and dry seasons afford less favorable conditions for 
rock decay, and the final product is blue clay. 
1 Hayes, C. Willard. Physiography and Geology of Region Adjacent to the 
Nicaragua Canal Route, Bull. Geol. Soc. Amer., vol. x (1899), pp. 285-348, Pls. 
XXX-XXXII. 
