1872.] 



SENATE— No. 249. 



15 



which I brought back from the Isthmus, and the material of 

 which has been given to the different Curators of the Museum. 



My geological and palaeontological collection is very rich in 

 good and characteristic specimens of the various rocks which 

 occur on the Atlantic and on the Pacific, and which form the con- 

 stituent parts of the dividing ridge between the two oceans. I 

 made geological surveys at three different parts of the Isthmus, 

 namely: 1st, between Aspinwall and Panama (Province of Pan- 

 ama) ; 2d, between the Gulf of Urabd, or Darien del Norte, and 

 the Gulf of St. Miguel, or Darien del Sur (Province of Darien) ; 

 3d, between the Napipi River and Cupica Bay (Province of 

 Choco) ; and collected as much material as possible, in order to 

 obtain- a clear insight into the geological structure of these re- 

 gions It was important for me, in this respect, to determine 

 the existence of several coal-beds on the Atlantic, near the Gulf 

 of Urabd, and to discover various tertiary deposits, full of fossil- 

 shells, up the Tuyra River, on the Gulf of St. Miguel on the 

 Pacific Ocean. 



The principal results which I have gained by this geological 

 examination of the Isthmus are the following : — 



1st. The Cordillera de los Andes changes its general charac- 

 ter in the Province of Choco ; while it strikes through the whole 

 of South America in a meridian direction, its general bearing 

 there is in the direction of the parallels. This strike is preserved 

 through the whole Isthmus, causing its curved form and the 

 sudden contraction of the continental mass. 



2d. The height of the Isthmus mountains is much less than 

 that of the South American Cordilleras, and decreases especially 

 between Panama and Aspinwall, where the whole orographical 

 character of the Isthmus undergoes a great change. The moun- 

 tainous system in the Province of Choc6, near Limon Bay, and 

 the internal part of Cupica Bay, has a geological character dif- 

 ferent from that of the Tuyra, and of the Chucunaque regions, 

 in the Province of Darien ; and this mountainous system differs 

 again, by its parallel arrangement, as well as by its petrographi- 

 cal composition, from that between Panama and Aspinwall. 

 Consequently the whole Isthmus consists of three systems differ- 

 ing from one another. 



3d. The Isthmus-Cordillera does not possess, in general, 



