264 BULLETIN": MUSEUM OF COMPAEATIVE ZOOLOGY. 



great and continuous pre-existing Cordilleran continental barrier. What 

 proof have we that this central barrier land may not have largely con- 

 tinued southward and continued to separate the oceans in Tropical 

 America, with the exception of a shallow passage or two barely sufficient 

 to permit the migration of littoral faunee 1 



Absence of Rocks indicating Off-shore Deposition in the Tropical Amer- 

 ican Mainland. — Had deep marine connection existed across the Isth- 

 mus of Panama in Tertiary time there should surely be preserved in the 

 region some rocks indicative of other than shallow deposition within this 

 hypothetic channel. Future observers may find them, but the expe- 

 rience of those of the past have not been fruitful in this direction. 

 ]S T owhere in the Tropical American mainland except along the marine 

 side of Yucatan has a single rock of Post-Cretaceous age been found 

 which indicates other than shallow near-shore deposition. The Empire 

 limestones are littoral and clearly composed of triturated oceanic de- 

 bris, alternating with impure sediments bearing plant remains. 



Absence of Known Tertiary Sediments on the Pacific Side of Tropical 

 America. — There is no positive record of Tertiary sediments having 

 ever been observed at any point on the vast stretch of the Pacific sea- 

 board of the Tropical American region south of the peninsula of Lower 

 California. Exploration has been deficient in this region however, 



Paleontologic Evidence of Marine Connection in Tertiary Time. — The 

 various fossiliferous horizons of the Tertiary series described in this 

 paper, in general are thoroughly Atlantic in their facies, the overwhelm- 

 ing majority of species of all the terranes being those found only within 

 the sediments of known Atlantic origin. A single terrane, however, fur- 

 nishes an admixture of Pacific species in the fauna which affords the 

 only direct paleontologic evidence resulting from our explorations which 

 indicates relationship between the two oceans past or present. Five 

 species of mollusks, noted by Dr. Dall in the Gatun (Vamos a Vamos) 

 beds of Eocene Tertiary, also occur in the Tejon Eocene of California. 

 The presence of these species is evidence that in the Claiborne Tejon 

 epoch there was at least shallow communication, and hence to this epoch 

 alone can the date of an interoceanic connection be assigned by direct 

 paleontologic evidence. 



Lack of Testimony showing that the Eocene Passage was other than 

 Shallow and Restricted. — None of the data presented by previous 

 writers, however, nor any of my own observations, are sufficient to 

 show that such a connection was of other than a shallow and re- 

 stricted character. 



