86 REVIEWS 



A comparison of the Miocene of America with that of Europe sug- 

 gests to Dr. Dall the following: 



The differentiation of faunas was well established before the beginning of 

 the Tertiary, and Eocene faunas in America show American characteristics 

 clearly, as compared with those of Europe. Other differences, suggesting migra- 

 tions, occur in the relative time of appearance of certain groups; as, for instance, 

 in America, the first influx of Nummulites is in the upper beds of the lower 

 Oligocene, just as they were about to disappear from the European fauna, 

 where they had flourished in myriads at an earlier epoch, though then unknown 

 west of the Atlantic. Thus we may expect and shall find, on an inspection of 

 the American Miocene, both differences and points of agreement. As in Europe, 

 so in America, the Miocene was a period of elevation of plication of the earth's 

 crust with its attendant vulcanism, of denudation of the recently elevated areas, 

 and the formation of extended areas of sediment, formed chiefly of clays, sands, 

 and marls, either consolidated into shales and sandstones, or remaining less 

 compacted. The elevation of middle America and the Antillean region, in 

 harmony with that of southern Europe, seems to have been more or less con- 

 stant, since no marine Miocene beds have been definitely recognized in this 

 area, and the antecedent Oligocene sediments were elevated several thousand 

 feet, North and South America were united, the island of Florida became attached 

 to the Georgian mainland, and the continent of North America on the whole 

 assumed approximately its present outlines. Some modification of the coast 

 line or sea bottom, supposedly in the vicinity of the Carolinas or possibly con- 

 nected with the elevation of the Antilles, diverted the warm currents corre- 

 sponding to the present Gulf Stream so far off-shore in the early part of the 

 Miocene as to permit of the invasion of the southern coast lines by a current 

 of cold water from the north, bringing with it its appropriate fauna and driving 

 southward or exterminating the pre-existent subtropical marine fauna of these 

 shores. This resulted in the most marked faunal change which is revealed by 

 the fossil faunas of the Atlantic coast of America subsequent to the Cretaceous. 

 A cool-temperate fauna for the time replaced the subtropical one normal to these 

 latitudes, and has left its traces on the margin of the continent from Martha's 

 Vineyard Island in Massachusetts south to Fort Worth inlet in east Florida, 

 and westward to the border of the then existing Mississippi embayment. 



The deep embayment of the Chesapeake region in Maryland and Virginia 

 has retained the largest and least-disturbed area of the marine Miocene sedi- 

 ments and given its name to them, as typical, on the Atlantic coast, of the faunal 

 remains of this character, which they contain. Contrary to the conditions 

 existing in Europe, in America no marked invasions by the sea or extensive 

 depressions of continental land are characteristic of Miocene time, though in 

 special localities the Miocene sediments transgress the remnants of the Eocene. 



Regarding temperature conditions Dr. Dall writes: 



