194 GEOLOGY. 



has hampered the whole physiographic conception of the period. It is prob- 

 able that this conception must be largely abandoned, and the broader view 

 of land aggradation, with lacustrine deposits as an incident, substituted, 1 

 and with this change will come some emendation of topographic and dynamic 

 interpretations. 



In applying a classification based on body deformation, some regard must 

 be had to the fact that while sea-withdrawal, as the result of increased capacity 

 of the sea-basins, is simultaneous the world over, continental deformations and 

 crustal foldings are more local and less nearly synchronous, for there is no agency 

 to combine and equalize their effects as in the case of the basins. Continental 

 deformations must be employed in the classification with some latitude, and 

 correlations based on them cannot be expected to have an equally high order 

 of exactness. Local advances and retreats of the sea due to local warpings 

 must be eliminated or neglected, in a general classification, for the reason that 

 they are local. If an attempt were made to shift the classification of the Tertiary 

 period to the basis here outlined, the changes would not be radical. 



After the deformative movements that closed the Mesozoic era, there seems 

 to have followed a rather protracted period of relative quiescence. In the early 

 part of this period, the area of the land was large, and its relief pronounced. 

 Secondary movements of adjustment through minor warpings, creep, and grada- 

 tion were in notable progress. During the later portion of the period, the 

 effects of these adjustments were felt in some notable extension of the sea over 

 the lower portions of the continental platforms. For North America this 

 transgression of the sea is represented in Fig. 418. The most notable feature 

 was the extension of the sea in the Mississippi embayment, represented by 

 the formations to be described later. This advance of the sea did not rival 

 the great transgressions of the Cretaceous and Jurassic periods, but the Atlantic 

 and Pacific seem to have joined between the two Americas, and the climatic 

 effects of a dominantly marine period seem to have prevailed, as indicated by 

 the warm-temperate life in middle and high latitudes. All of this seems to 

 constitute a natural period, embracing what is included in the Eocene and the 

 Lower Oligocene (Vicksburgian) . 



In North America, this period was closed by a withdrawal of the sea from 

 both the Atlantic and Pacific borders of the continent, and by notable crustal 

 deformations in some parts of the western mountain region. At the same time, 

 Florida, which had been submerged and the site of calcareous sedimentation, 

 was partly emerged. Farther south, the changes were even more important, 

 for they appear to have interrupted the connection between the Atlantic and 



l See Davis, Science, N. S., Vol. VI, p. 619, 1897, and Proc. Am. Acad. Arts and 

 Sci., Vol. XXXV, p. 345, 1900; and Mus. Comp. Zool.-Geol. Surv., Vol. VI, pp. 43, 45-7, 

 and 48; Gilbert, Pueblo folio, U. S. Geol. Surv., 1897, and Nat. Geog. Mag. Vol. IX, pp. 

 308-317, 1898; Matthew, Am. Nat., Vol. XXXIII, p. 403, 1899; Hatcher, Proc. Am. 

 Phil. Soc, Vol. XLI, 1902, Rev. Jour, of Geol., Vol. XI, p. 92, and Johnson, W. D., 

 21st Ann. Rept. U. S. Geol. Surv., Pt. IV. 



