200 CALIFORNIA ACADEMY OF SCIENCES [Proc. 4th Ser. 



the Isthmus although they recognize the presence of stream- 

 laid deposits resting upon rocks bearing a Bowden fauna. The 

 faunal evidence along the various lines discussed above in no 

 manner indicates any recent connections. 



Dr. T. W. Vaughan recently published a professional paper, 

 The Reef-Coral Fauna of Carrizo Creek, Imperial County, 

 California, and Its Significance, which gives decided support 

 to Spencers views. Vaughan's conclusions concerning the 

 interesting coral fauna obtained from the head of the Gulf 

 of California are: 



"1. The Carrizo Creek reef-coral fauna is Atlantic, not 

 Pacific, in its affinities. 



2. During Eocene and Oligocene time there was connection 

 between the Atlantic and Pacific oceans across Central America, 

 and there was no sharp differentiation between the Atlantic 

 and Pacific faunas. 



3. Upper Oligocene (Apalachicolan) time was closed by 

 diastrophic and other geologic events of profound importance, 

 which separated the Atlantic from the Pacific Ocean l3y form- 

 ing a land area extending from North to South America. Dur- 

 ing Miocene time sharp differentiation between the Atlantic 

 and Pacific faunas took place, largely by the extinction of the 

 Pacific elements in the Atlantic area. 



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

 its affinities, and since Pliocene time there has been only minor 

 modification of the coral fauna in the western Atlantic, the 

 Gulf of Mexico, and the Carribbean Sea. 



5. The fauna of Carrizo Creek is related to 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 

 Pacific faunas there was in upper Miocene or Pliocene time 

 inter-oceanic connection, which permitted the Atlantic fauna 

 to extend into the Gulf of California and up to its head, and 

 conditions not yet understood excluded the Pacific fauna from 

 the area. 



7. The locus of the inferred interoceanic connection is not 

 known. It was probably in the region of the Isthmus of 

 Tehauntepec, or farther southeast." 



