616 T. W. VAUGHAX GEOLOGIC HISTORY OF CEXTRAL AMERICA 



development and distribution of the natural order Luguminosse," * and 

 "The geological history of the Australian flowering plants," ^ by C. E. 

 Andrews; and "Plants, seeds, and currents in the West Indies and 

 Azores," by H. B. Guppy.*^ These three authors agree in their main thesis, 

 nameh^, that vertebrates and plants have spread from northern areas ra- 

 dially southward over Africa, South America, southeastern Asia, Malay- 

 sia, and Australasia. They all deny direct land connection, at least since 

 Paleozoic or early Mesozoic time, between Africa and South America and 

 between South America and Australia, and they question there ever hav- 

 ing been any such bridges. Furthermore, they all agree, explicitly or im- 

 plicitly, in the essential permanence of the continents and of the great 

 oceanic basins. There are other points of agreement, but these are the 

 ones I wish particularly to emphasize in this connection. Although I 

 may not accept every detail of the conclusions of these authors, it is my 

 belief that their main contention is incontrovertible. 



All geologic evidence knoAvn to me supports the theory of the perma- 

 nence of continents and oceanic basins, but the validity of this theory 

 does not exclude there having been great differential crustal movements 

 in some areas. As I shall speak of certain earth blocks that, in my opin- 

 ion, have changed their position with reference to sealevel, I wish to re- 

 mind 5^ou that faults and folds causing great vertical and horizontal 

 displacement of strata now above sealevel are known to all geologists, and 

 that it is reasonable to expect in other areas of disturbance that down- 

 thrown blocks or the synclines of folds lie below, while only the upthrown 

 blocks or the anticlines stand above ocean level. 



Geographic Relatioxs of the three Americas 



The boundaries of the Gulf of Mexico and the Caribbean Sea form a 

 parallelogram; those on the north and south extend along east and west 

 lines, those on the east and west are northwest to southeast, while the 

 basins are separated by east and west structures. There are two land- 

 locked basins, except that between Florida and Trinidad relatively shal- 

 low passages between land areas connect with the Atlantic Ocean. The 

 two basins are separated by structures transverse to the continental trend 

 in Yucatan and Cuba, and the Gulf of Mexico is a simple while the 

 Caribbean Sea is a compound basin. 



* Now South Wales Roy. Soc. Proc, vol. 48, 1014, pp. 33.3-407. 

 = Amer. .lour. Sci.. 4th ser., vol. 42, 1910, pp. 171-232. 



" Published by Williams and Norgate, London, 1917, pp. 531, 3 maps and a frontis- 

 piece. 



