Vol. VII] DICKERSON— ANCIENT PANAMA CANALS 205 



might show the relations between the Magdalena Bay fauna 

 and that of the Cahfornia Miocene. 



All investigators have recognized a number of living species 

 in this fauna, Gabb 30 to 40 per cent, Moore 8 to 9 per cent, 

 Guppy 20 per cent. Brown and Pilsbry about 5 per cent. These 

 percentages are all greater than is exhibited in the Oligocene 

 of the Pacific Coast and the faunal relations to recent fauna 

 corresponds to our California Miocene. The correct value may 

 be about 5 to 10 per cent. From all evidence available a 

 Miocene age for the Bowden beds appears to be correct. 



With wide openings between the Pacific and Atlantic in the 

 Central American region, the trade winds of Miocene time 

 probably drove the waters of the Atlantic through these pass- 

 ages and no Gulf Stream existed. On this account, sharply 

 defined climatic zones were present on both coasts of United 

 States and the faunas of the tropics were sharply separated 

 from those of the temperate regions. This oceanic current 

 condition accounts quite satisfactorily for the scantiness of 

 species common to the California middle Miocene and the 

 Magdalena Bay fauna on the west coast. 



In summary: The Panama Portal was closed during Cre- 

 taceous time and this gateway was not opened until upper 

 Eocene time. During a period of widespread uplift — Oligo- 

 cene time — the Antilles were probably connected with southern 

 Florida and possible Central America. Following this emer- 

 gent stage, a wide submergence occurred during Miocene time, 

 marked by the Bowden horizon. At this period North and 

 South America were disconnected and wide straits in Central 

 America were formed. Since the Miocene, the Panama portal 

 has remained closed until Colonel Goethals and his men 

 trenched the narrow barrier by the Panama Canal. 



