Isthmus Barriers Separating Fish Faunas 275 



"In 1 88 1, Dr. Paul Fischer discussed the same question in 

 his 'Manual de Conchy liologie, ' pp. 168, 169, in a section on 

 the Molluscan Fauna of the Panamic Province, and reached 

 the same general conclusions. He says : ' Les naturalistes 

 Americians se sont beaucoup preeoccupes des especes de Panama 

 qui paraissent identiques avec celles des Antilles, ou qui sont 

 representatives. P. Carpenter estime qu'il en existe 35. Dans 

 la plupart des cas, 1'identite absolue n'a pu etre constantee 

 et on a trouve quelques caracteres distinctifs, ce qui n'a rien 

 d'etonnant, puisque dans 1'hypothese d'une origine commune, 

 les deux races pacifique et atlantique sont se'pare'e depuis la 

 periode Miocene. Voici un liste de ces especes representatives 

 ou identiques.' Here follows a list of 20 species. 'Mais ces 

 formes semblables,' he says, 'constituent un infime minorite 

 (3 per cent.).' 



"These facts have a very important bearing upon certain 

 geological questions, particularly upon the one concerning the 

 cold of the Glacial period. 



" In Dr. G. Frederick Wright's recent book, 'The Ice Age in 

 North America,' eight different theories as to the cause of the 

 cold are discussed. The particular theory which seems to him 

 quite reasonable is that one which attributes the cold as due 

 to a change of different parts of the country, and a depression 

 of the Isthmus of Panama is one of the important changes he 

 considers. He says : ' Should a portion of the Gulf Stream be 

 driven through a depression across the Isthmus of Panama into 

 the Pacific, and an equal portion be diverted from the Atlantic 

 coast of the United States by an elevation of the sea-bottom 

 between Florida and Cuba, the consequences would necessarily 

 be incalculably great, so that the mere existence of such a pos- 

 sible cause for great changes in the distribution of moisture 

 over the northern hemisphere is sufficient to make one hesitate 

 before committing himself unreservedly to any other theory; 

 at any rate, to one which has not for itself independent and 

 adequate proof.' 



"In the appendix to the same volume Mr. Warren Upham, 

 in discussing the probable causes of glaciation, says: 'The qua- 

 ternary uplifts of the Andes and Rocky Mountains and of the 

 West Indies make it nearly certain that the Isthmus of Panama 



