PALEOGEOGRAPHIC SUMMARY 627 



The mammals furnish more evidence of this kind than 1 am present- 

 ing here^ and Barbour and. Stejneger, from their study of reptiles, have 

 reached similar conclusions, which accord with the tectonic history of the 

 region, namely, that in late Tertiary, probably Pliocene, time the West 

 Indian Islands as we know them were produced by block-faulting Avhich 

 broke into pieces a far more extensive land area. Dr. W. D. Matthew 

 does not agree with the postulated connections from Cuba to Yucatan, 

 from Jamaica to Honduras, and from Anguilla to South America.^* The 

 method of distribution of the terrestrial organisms must be left for the 

 consideration of those best versed in such subjects, and I am only war- 

 ranted in saying that at present there is no knoM^n geologic evidence 

 against a late Miocene or early Pliocene connection from Anguilla to 

 South America or from western Cuba and Jamaica to Central America. 



Following this geologically late episode of cataclysmic faulting, it ap- 

 pears that in some areas there was minor submergence of the margins of 

 some of the West Indian Islands and parts of Central America — for in- 

 stance, Panama and Costa Eica. 



According to Hill, the volcanoes of the Windward Islands date back at 

 least to the Eocene. He says : 



"After the Miocene, vuleanism became quiescent in the Great Antilles and 

 the Coastal Plain of Texas, but has continued to the present in the four great 

 foci of present activity — southern Mexico, the northern Andes, Central Amer- 

 ica, and the Windward Islands. In the last two regions mentioned, the greater 

 masses of the present volcanic heights were piled up before the Pliocene, and 

 the present craters are merely secondary and expiring phenomena." 



The last important shift in position of strand-line along the Atlantic 

 coast of the United States and around the shore of the Gulf of Mexico 

 and the Caribbean Sea has been by submergence of land areas, but subse- 

 quent to this there has been local emergence, often accompanied by minor 

 tilting or warping. 



Except vuleanism, the following table presents a succinct summary of 

 the major events considered in the foregoing remarks. My primary in- 

 tention has been to characterize biologically and to correlate tlie marine 

 formations of the Canal Zone and the geologically related areas in Central 

 America and the West Indies, and to lay particular stress on the succes- 



" Miller says in a letter to me : "Matthew's argument seems to me to have two very 

 weak spots in it : He minimizes the variety of structure shown by the W. I. rodents, 

 and he hanks altogether too heavily on what we don't know — that is, on the apparent 

 absence of ungulates and other things that ought to be present in a continental fauna. 

 When it is remembered that all but three of these ten genera of rodents and the insec- 

 tivore NesopJiontes were unknown tlve years ago, we ought to be very shy of predicting 

 what the next digging will not turn up. But it seems to me that what you have quoted 

 of mine contains about all the comment I need to make in print. G. S. M. Jr." 



