220 BULLETIN: MUSEUM OF COMPAEATIYE 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 Jose, 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, a 

 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, 1 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 Sjogren while in San 

 Jose, 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 

 Jose to Cartago, and together we ascended the volcano of Irazu, and 

 made the journey from thence to Port Limon. I am 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, 

 Esq., F.G.S., F.C.S., etc. With an Appendix by W. II. Huddleston, Esq., etc. 

 Quarterly Journal Geol. Soc. London, 1882, pp. 328-340. 



