JuLy 28, 1899.] 
bearing on the location of a canal route, is 
the great depression which extends diago- 
SCIENCE. 99 
ent to former divides and coast lines are 
shown on the accompanying map. 
of the 
NICARAGUA CANAL REGIO 
showing geologically recent changes in ( 
OUTLINE MAP (i 
N 
SN 
the position of the coastline and divides. 
Pacific coastline at the end of the post- Ternary baseleveling period -\----- 
Se 
5 
BWEFIELDS 
\s , SAN CARLOS 
p CASTILLO 
Former continental divide --++ 
nally across the isthmus, holding the Lakes 
Managua and Nicaragua and their outlet 
the San Juan River. Its southwestern 
margin is formed by the lofty volcanic 
range of northern Costa Rica, while it is less 
definitely limited on the northeast by the 
Chontales hills, which extend from the Ca- 
ribbean coast westward to the lakes. The 
Nicaraguan Depression, as above outlined, is 
not a simple river valley; although itis now 
occupied by a single trunk stream and its 
tributaries. Except for the constructional 
volcanic slopes at its southern margin, the 
depression is due entirely to ordinary 
stream erosion. During its formation, how- 
ever, the continental divide occupied a posi- 
tion near the axis of the isthmus, while the 
western coast was indented by a deep bay 
reaching to the center of the present basin 
of Lake Nicaragua. The relations of pres- 
Considering a broad belt extending across 
the isthmus and embracing the Nicaraguan 
depression, three distinct types of topog- 
raphy are encountered, viz. : 
Old-land areas with maturely developed 
degradational surfaces. 
Recent flood-plains and deltas with still- 
forming aggradational surfaces. 
Recent voleanic cones and plateaus with 
slightly modified constructional surfaces. 
The old-land occupies much the larger 
portion of the region represented on the ac- 
companying map. It forms the greater 
part of the Nicaraguan depression and ex- 
pands northward between the divergent 
lines of the Caribbean coast and the Nica- 
ragua-Managua lake basins. It also forms 
the narrower part of the land strip between 
lake Nicaragua and the Pacific. This old- 
land surface appears to have been above 
