ABSTRACTS OF PAPERS 231 



of Teliuantepec may be of Eocene age. The faunal relationships between the 

 Mexican Coastal Plain and the Tejon of California indicate that there were 

 straits which were probably situated in the Isthmus of Tehuantepec during 

 Upper Eocene time. The lack of a close relationship between the faunas of 

 the Martinez-Eocene stage and the Midway indicates the opposite conclusion. 

 The evidence concerning the Lower Oligocene or Yicksburg stage is quite de- 

 ficient and it is impossible to determine any connections at this time. 



Spencer postulates Pliocene canals through the Isthmus of Tehuantepec. 

 Bose and Toula, who have studied the Isthmus of Tehuantepec, disagree en- 

 tirely with Spencer's geologic data, and state that it is impossible to trace 

 marine terraces across the Isthmus, although they recognize the presence of 

 stream-laid deposits resting on rocks bearing a Bowden fauna. The faunal 

 evidence along the various lines discussed below in no manner indicates any 

 recent connections. 



Faunal relations of the living mollusks, fishes, echinoderms, and corals from 

 the Panamic and Caribbean provinces indicate that no connection existed be- 

 tween the Atlantic and Pacific during the Pliocene or Pleistocene. A study of 

 the mammals of North and South America demonstrates that a barrier was 

 present during the Miocene. The recent Panamic marine invertebrate fauna 

 is related to that of the Bowden horizon of Jamaica, and straits probably ex- 

 isted at various times during the deposition of the Bowden beds. 



According to Hill, during Cretaceous time the majoi- islands of the Antilles 

 were started on the crests of oceanic volcanoes. These land-masses thus built 

 up were submerged in part and the sediments deposited from their erosion 

 contain a fauna of Upper Cretaceous age. At the end of Cretaceous time these 

 strata were folded along a northwest-southeast axis. In late Eocene and 

 early Oligocene time a profound regional sub.sidence occurred, during which 

 all but the highest tips of the Antilles were covered by the waters of the 

 Caribbean. This subsidence was followed by an uplift in Oligocene time, dur- 

 ing which great orogenic movements along east-west axes took place. This 

 was the stage, if at all, of an Antillean continent. Possibly many of the larger 

 islands were connected at this time, and the southern portion of Florida may 

 have been linked with this large Antillean island. This event was succeeded 

 by another great submergence, and portions of Mexico and Central America, 

 as well as the major portions of the Antilles, were largely covered with oceanic 

 waters — the Bowden stage. 



According to the work of Scott and Matthew in the study of recent and 

 fossil mammals, any connection of the mainland with the Antilles is very 

 unlikely. The species of small sloth found in the Pleistocene beds of Cuba 

 sprang from a single form which may have emigrated there by way of a raft. 

 Scott shows that during Miocene time the mammalian fauna of North and 

 South America were entirely distinct. These facts indicate that a period of 

 wide-spread submergence occurred during the Miocene, and on this account the 

 beds bearing the Bowden fauna might well represent this era of subsidence. 



Recently a fauna collected from the vicinity of Magdalena Bay, Lower Cali- 

 fornia, was submitted to Dr. Ralph Arnold and Dr. B. L. Clark for determina- 

 tion. This fauna contains I'cctcn condylomatus Dall, of the Chipola horizon 

 of Florida and the Tuxpan beds of Mexico ; Pecten oxygomum optimum Brown 

 and Pilsbry, of the Gatun beds, Panama ; Rxta gihhosa Gabb, of the Peruvian 

 XVI— Bull. Geot.. Soc. Am., Vol. 28, 1916 



