16 MUSEUM OF COMPARATIVE ZOOLOGY. [Apr. 



table-lands of so large an extent as those which are frequently 

 encountered in the South American Cordillera, as well as in 

 Central America. This is a very important fact, if we bear in 

 mind that these high table-lands on the western coast alone 

 make it possible for a white man to work with endurance in the 

 tropics, and to cultivate with success all those natural products 

 which create tropical commerce. This orographical fact, prop- 

 erly understood and applied, is the key to an explanation of a 

 great many things in the past history of South America, of the 

 Isthmus and of Central America. 



4th. We possess palseontological proofs, preserved in the ter- 

 tiary strata of the Tuyra River on the Pacific slope, on the one 

 hand, and in the tertiary deposits from Empire Station to 

 Monkey Hill, along the Panama Railroad on the Atlantic slope, 

 on the other hand, which show us that at least two channels, — one 

 between the Gulf of St. Miguel and the Gulf of Urabd, the other 

 between Panama and Aspinwall, — existed up to the later tertiary 

 period, by which both oceans mingled their waters. This fact 

 is important for an understanding of the geographical distribu- 

 tion of the present botanical and animal life. 



5th. The upheaval of the Pacific Cordillera belongs to the 

 later eruptive period, and its rocks belong to the petrographical 

 famihes of the trachyte and the basalt ; while the San Bias 

 Cordillera, of the Atlantic slope, belongs to an older geological 

 period, and is composed of the older crystalline rocks, — granite, 

 syenite and diorite. The northern Atlantic slope was conse- 

 quently already upheaved and in a state of tranquillity when 

 the waters of the South Sea still covered the whole area which 

 forms at present the Pacific slope. If after this we take into 

 account the constant disintegrating effect of the north-eastern 

 trade-wind, saturated with the moisture of the Caribbean Sea, 

 we shall understand how it was possible that the rocks of the 

 Atlantic slope could be so greatly decomposed, and could furnish 

 afterwards the material of a fertile soil which had the power to 

 produce a most gorgeous vegetation. 



I have given, so far, the positive results which have been gained 

 up to the present time for the Museum by the expedition. But 

 I can add that I have also gained for our Museum, during this 

 journey, several friends residing on the Isthmus, as well as in 



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