352 Scientific Intelligence. 



capable of leaving traces in the shape of fossils, under conditions 

 not greatly different from those of the present day, if situated in 

 the arctic or boreal region, would comprise about 250 species; in 

 the cool temperate region about 400 species ; in the warm temper- 

 ate, about 500 species; and in the tropical region, not less than 

 600 species" (page 27). The clear recognition of these local and 

 general conditions as affecting the life of the globe prepares the 

 way for a distinct advance in practical geologic correlation. 

 Many years ago Barrande developed the conception of colonies, 

 and subsequently Huxley wrought out the idea of homotaxis to 

 explain the recurrence of allied faunas in different regions at dif- 

 ferent periods ; and in this country Calvin, followed in greater 

 detail by H. S. Williams, called attention to the changes in Pale- 

 ozoic faunas evidently accompanying changes in character of sed- 

 imentation. These paleontologic researches, in common with mod- 

 ern researches in biology, show that life has not flowed in an 

 even stream but has been constantly affected by local and general 

 environmental conditions. Dall and Harris go further than their 

 paleontologic predecessors and, thanks to the exceptional oppor- 

 tunity afforded by the study of relatively recent deposits, are able 

 clearly to formulate a part at least of the homotaxial conditions. 

 Thus their memoir is an important contribution not only to geol- 

 ogy through paleontological method but also to general biology, 

 and may be considered an exposition of the principles of homotaxy. 

 The authors' final conclusion concerning the applications and 

 limitations of paleontology as a basis for geological correlation is 

 thus stated : " While paleontology holds the key to the problems 

 of local and comparative stratigraphy, yet no study of paleontol- 

 ogy that neglects the broad and general stratigraphic changes 

 which accompany the development of the continental border as a 

 whole is calculated to afford results of permanent value" (page 31). 



The second chapter is a summary of knowledge concerning the 

 Neocene of the Atlantic and Gulf coasts, arranged by states and 

 illustrated by a special map of Florida and a general map show- 

 ing the distribution of the Neocene formations of the country; 

 while the third chapter is a general discussion of the relations of 

 the Neocene deposits of the eastern province. 



After showing that the Pliocene of North America, though 

 homotaxial is probably not wholly synchronous with that of 

 Europe and that the end of the American Miocene as generally 

 understood, was marked by a great movement in elevation which 

 united North and South America and joined the island of Florida 

 to the mainland of Georgia, the authors adopt the culmination of 

 this elevation as the physical event terminating the Miocene and 

 from which the American Pliocene extends until, in its turn, ter- 

 minated by the inauguration of the Glacial epoch. 



Having thus limited the major divisions of the Neocene, the 

 subdivisions of Miocene and Pliocene are discussed. The term 

 Miocene in the United States has hitherto been understood 

 to include the epoch covering the deposition of the well known 



