220 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
and the coast swamp level, — the two last mentioned features indicating 
two successive continental uplifts without serious deformation. 
The outlying islands are not coralline, like many of the Caribbean, 
not a single evidence of either growing or elevated reef structure having 
been seen. Neither are they volcanic cones or craters which grew up 
singly from the ocean, but they are composed of the same masses 
of ancient, greatly eroded basic rocks as the mainland, and they 
have evidently participated in the identical vicissitudes of uplift and 
subsidence. Comparing them from shipboard with the adjacent main- 
land, one cannot escape the conclusion that they were once continuous 
with it, or that they were once parts of each other. 
PART IV. 
A Continental Section across Costa Rica in the Longitude 
of San José, from Punta Arenas to Port Limon. 
In order to obtain further light upon the structure of the Isthmus, 
I made an overland section across Costa Rica from Punta Arenas, : 
Pacific port on the Gulf of Nicoya, to Port Limon, on the waters of the 
Caribbean. 
The section, or rather portions of the section, I will describe through 
Costa Rica has been the subject of several publications,’ but it is one of 
such magnitude and grandeur, that much still remains to be recorded 
concerning it, and I shall point out several new and important elements 
which have hitherto been overlooked. 
It was also my fortune to fall in with Mr. Ahe Sjógren while in San 
José, a young mining engineer of unusual acumen, who had been for two 
years industriously studying the region, and who had spent much of the 
time upon the peninsula of Nicoya. He accompanied me from San 
José to Cartago, and together we ascended the volcano of Irazu, and 
made the journey from thence to Port Limon. Iam indebted to him 
for the excellent section of the disturbed Tertiaries of the Atlantic 
slope, from Las Animas to Las Lomas, which is printed herewith 
1 One of these sections, by George Attwood, Esq., is an admirable sketch of the 
principal phenomena of the section as far east as the volcano of Turialba, which 
marks the border of the Atlantic declivity. He does not touch upon the latter 
subject, however. On the Geology of a Part of Costa Rica, by George Attwood, 
Ева, F.G.S., F.C.S., ete. With an Appendix by W. H. Huddleston, Esq., etc. 
Quarterly Journal Geol. Soc. London, 1882, pp. 528-340. 
