200 PROCEEDINGS OF THE PALEONTOLOGTCAL SOCIETY 



A second paper on fossil corals and tlieir bearing on Tertiary paleo- 

 geography was presented next and was illustrated by lantern slides. 

 Discussed by Messers. Schnchert, Graban, and the anthor. 



REEF CORAL FAUNA OF CARRIZO CREEK, IMPERIAL COUNTY, CALIFORNIA, 

 AND ITS SIGNIFICANCE 



BY T. WAYLAND V AUG HAN 



(Abstract) 



The paper was an abstract of a short monograph entitled "The reef -coral 

 fauna of Carrizo Creek, Imperial County, California, and its geologic signifi- 

 cance," in press as Professional Paper 98-T of the United States Geological 

 Survey. 



Carrizo Creek, along which the corals were obtained, is in the western part 

 of Imperial Valley, about 15 miles north of the Mexican boundary and about 

 20 miles southwest of the southern end of Salton Sea. The geologic section 

 comprises (1) a basal complex of granites and metamorphic rocks, (2) ande- 

 site extruded over the eroded surface of the basal complex, (3) a marine 

 sedimentary series of clays, sands, and conglomerates which rest on the eroded 

 surface of the underlying rocks and in the lower part of which are abundant 

 reef corals, and (4) Pleistocene lake beds. 



The conclusions resulting from the study are as follows : 



1. The Carrizo Creek reef-coral fauna is Atlantic, not Pacific, in its attinities. 



2. During Eocene and Oligocene time there was connection between the At- 

 lantic and Pacific oceans across Central America, and there was no sharp dif- 

 ferentiation between the Atlantic and Pacific fauna. 



3. Upper Oligocene (Apalachicolan) time was closed by diastrophic and 

 other geologic e^-ents of profound importance, which separated the Atlantic 

 from the Pacific Ocean by a land area extending from North to South America. 

 During Miocene time the sharp differentiation between the Atlantic and Pacific 

 faunas took place, largely by the extinction of the Pacific elements in the 

 former fauna. 



4. The Pliocene coral fauna of Florida is purely Atlantic in its aflSnities, 

 and since Pliocene time there has been only minor modification of the coral 

 fauna in the western Atlantic, the Gulf of Mexico, and the Caribbean Sea. 



5. The Carrizo Creek fauna is related to the Pliocene and post-Pliocene 

 faunas of Florida and the West Indies and can scarcely be older than Lower 

 Pliocene. 



6. Subsequent to the differentiation between the Atlantic and the Pacific 

 faunas there was interoceanic connection in Upper Miocene of Pliocene time 

 which permitted the Atlantic fauna to extend into the Gulf of California and 

 up to its head, and conditions ^vhich we do not understand excluded the Pacific 

 fauna from that area. 



7. The locus of the inferred interoceanic connection is not known. It was 

 probably in the region of the Isthmus of Tehuantepec or farther southeastward. 



