PRINCIPLES OF PALEONTOLOGIC CORRELATION 69 1 



migration due to the removal of barriers. 1 It would seem, then, 

 that changes in physical geography have been the chief cause, 

 not only of migration, but also of extinction of faunas ; and this 

 becomes all the more probable when we reflect that species have 

 not been extinguished contemporaneously over the earth. 



Remarkable cases of survivals of types have long been known, 

 as of Trigonia in the Australian waters, and of Pholadomya in the 

 Antilles. Survivals of faunas, too, are continually coming to 

 light. A number of species that on the west coast of the United 

 States are known only as fossils in Pliocene and Quaternary 

 strata, are still living elsewhere. Dall 2 has shown that a large 

 proportion of the Pliocene and even Miocene invertebrates of 

 the southeastern states are still found living in the archibenthal 

 region off the present coast. Similarly, it has been shown by 

 Walcott 3 that in the Great Basin Carboniferous province many 

 Devonian types persisted long after they had become extinct 

 elsewhere, and this has been used by H. S. Williams 4 to explain 

 the reappearance in the Mississippi valley St. Louis beds of a 

 fauna previously thought to have been extinct since the very 

 beginning of Carboniferous times. 



Dr. David Brauns 5 cites from the late Pliocene or early Pleis- 

 tocene of Japan a large number of species that are still flour- 

 ishing on the western coast of America, and some are found liv- 

 ing there that in western America are known only as fossils. 

 Thus in the future some confusion might originate by correlating 

 these beds with those now forming. 



It is well known that during the Upper Carboniferous there 

 flourished in India, South Africa, and Australia the Glossopteris 

 flora, a type that in other regions was characteristic of Mesozoic 

 instead of Paleozoic beds. Waagen 6 has suggested that the 



1 J. P. Smith: Jour. Geol. Vol. Ill, 1895. Mesozoic Changes in the Faunal 

 Geography of California. 



2 Bull. Mils. Comp. Z06L, Vol. XII, No. 6, p. 186. 

 3Mon. VIII, U. S. Geol. Survey. 



4 Amer, Jour. Sci. Ill Ser., Vol. XLIX, pp. 94-101. 



s Mem. Science Dept. Univ. of Tokio, No. 4, 1881, p. 77. 



6 Pal. Indica. Salt Range Fossils. Geological Results, p. 240. 



