Geology. 353 



beds extending from New Jersey to Georgia which have been 

 variously subdivided by Heilprin and others. It is now shown, 

 however, that this Miocene, for which the name Chesapeake 

 is adopted, represents only a part of the geological column 

 between the Eocene and Pliocene. It was preceded by a 

 division of at least equal importance, represented on the Gulf 

 coasts by a greater thickness of strata, which encloses a fauna 

 closely related to the Haitian and Jamaican Miocene, and of a 

 distinctly tropical facies. Traces of this fauna are found in New 

 Jersey, but it is in Florida and on the north shores of the Gulf of 

 Mexico that it is found, uneroded, in its full development. 



For the epoch covering its deposition and including the Chat- 

 tahoochee and Tampa groups the name of Chipola has been pro- 

 posed by Dall in a later publication.* The transition from the 

 Chipola to the Chesapeake fauna is abrupt and is shown to involve 

 a marked refrigeration of the Gulf of Mexico, f 



The Pliocene of Florida shows a subtropical reaction in the 

 matter of temperature, perhaps promoted by the closure of the 

 strait which in Miocene times separated the peninsula from 

 Georgia. The age of the South American fossil mammals which 

 are found in Florida is determined by their discovery, as an- 

 nounced here, between mid-Pliocene shell limestones ; and, inci- 

 dentally, the peninsula of Florida is shown to consist of a central 

 trough or ancient lake-basin, for which the name of De Soto is 

 proposed, with low but unmistakable parallel folds on either side 

 of the peninsula. The entire peninsula is built up of marine or- 

 ganic sediments and contains no minerals of other origin. Degra- 

 dation has proceeded by solution rather than erosion, and reasons 

 are given for supposing that the peninsula, since the Miocene, has 

 maintained a remarkable stability and has not submitted to any 

 serious changes of level. 



Two chapters are devoted respectively to detailed description 

 and general discussion of the Neocene formations of the Pacific 

 coast of the United States and Canada, including Alaska ; the lat- 

 ter being illustrated and elucidated by a convenient " Table indi- 

 cating conditions existing during Cenozoic time in regard to 

 changes of level " and the prevalence of volcanic emissions on the 

 northwest coast (p. 278). The most interesting fact discussed is 

 the age of the so-called Miocene leaf-beds of Alaska and the 

 northwest coast which may probably turn out to be of Eocene 

 age. The "Ground ice formation" of northern Alaska has also a 

 peculiar interest. 



* Trans. Wagner Inst, vol. iii, p. 307, Jan., 1892. 



\ This writing- gives opportunity for the correction of an erroneous expression 

 by the writer, printed before the appearance of the above memoir (" The Lafayette 

 Formation," 12th Annual Report of the Director of the U. S. Geological Survey, 

 1892, page 411). The faunal change recognized by Dall and Harris has no con- 

 nection with differences made by Heilprin the basis of a separation of the Atlantic 

 coast Miocene into a " Marylandian " and " Virginian " series. The latter simply 

 relate to proposed subdivisions of the Chesapeake formation, on the principle of 

 percentages of survival. 



