THE EOCENE PERIOD. 195 



the Pacific in tropical latitudes, diverting the equatorial current of the Atlantic 

 to the northern part of that ocean. These changes, with their attendant effects 

 on climate, influenced the character and distribution of the life. The initial 

 bowing of the Pyrenees and some other mountains in southern Europe is assigned 

 to this time. It is therefore tentatively assumed that there was a sufficiently 

 general deformative movement at the close of the Eocene to mark the end of a 

 a natural period. 



The time occupied in these movements and in the secondary results which 

 immediately followed may be regarded as a transitional stage, and referred to 

 the Oligocene, with the rank of an epoch rather than a period. In the lower 

 Mississippi region, the deposition of this epoch took on a terrestrial and a marine 

 phase, the terrestrial recorded by a part of the Grand Gulf beds, containing 

 land plants with occasional fresh-water molluscs; the marine by the Chatta- 

 hoochie formation. Inland, the White River beds of the Great plains are referred 

 to the same epoch. Matthew 1 urges that these are of eolian origin, practically 

 an ancient loess, which, if true, implies something of aridity in the west, a con- 

 dition in harmony with the rapid evolution of the solid-hoofed animals adapted 

 to dry plains, with the gypseous deposits in the Grand Gulf series, and with the 

 notable gypsum formations of the Paris basin, referred to the Oligocene. In 

 these are seen the natural consequences of an epoch of land extension. 



The true Miocene, according to Dall, 2 was ushered in by a marked change 

 in the temperature of the waters of the Atlantic coast, attributed to a northern 

 current, and resulting in the sharpest faunal change in the Tertiary series of 

 the Atlantic coast. Apparently this must mean more than a mere shifting of 

 preexisting currents, for a cold current so far south can hardly be referred to 

 North Atlantic waters, when magnolias and many other trees now confined to 

 the warm temperate zone were growing in Greenland and the Arctic regions 

 generally. Heer has identified a large flora of forms that now imply a tem- 

 perate climate, in latitudes of 60° to 80°, which he refers to the Miocene. 3 The 

 correctness of this reference is questioned on other grounds, and the cold Mio- 

 cene current on the southern coast of the United States, colder than that of 

 to-day, makes such a reference highly improbable. The Miocene cold current 

 seems to imply an important climatic change affecting the north Atlantic, and 

 adds strength to the evidences above cited of the deformative action closing the 

 Eocene. The flora of Europe referred to the early Miocene is not in harmony 

 with this supposed cooler condition, since it embraces forms now representative 

 of warm latitudes; but during the period a marked change in the direction of 

 the existing flora took place. 



During the Miocene, the sea again advanced upon the land on both the Atlantic 

 and Pacific coasts, though not greatly beyond the present limits, and chiefly 

 in the Maryland-California latitudes; hence this may be regarded as an inter- 

 deformative stage, and as extending to the next general deformative movement. 



1 Am. Nat., Vol. XXXIII, p. 403, 1899. 



8 18th Ann. Rept. U. S. Geol. Surv., 1898, p. 329; see also other papers postea. 



"Flora Fossilis Arctica, Vol. I, pp. 161-166. 



