MARYLAXD GEOLOGICAL SURVEY cxli 



those of a more temperate type while the climate of the temperate zone, 

 indicated by the land animals and vegetation became noticeably cooler 

 than it had been during the Miocene epoch. 



Having thus indicated the salient characteristics of the Miocene epoch 

 as understood by European geologists, it becomes possible to compare 

 them with those of the epoch referred to the Miocene in North America. 

 The differentiation of faunas was well established before the beginning 

 of the Tertiarv, and Eogene faunas in America shovv^ American charac- 

 teristics clearlj^, as compared with those of Europe. Other differences, 

 suggesting migrations, 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 dis- 

 appear 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 constant, since no marine Miocene beds have 

 been definitely recognized in this area, and the antecedent Oligocene sedi- 

 ments were elevated several thousand feet, :Nrorth and South America 

 were united, the island of Florida became attached to the Georgian main- 

 land, and the continent of North America on the whole assumed approxi- 

 mately its present outlines. Some modification of the coast line or sea- 

 bottom, supposedly in the vicinity of the Carolinas or possibly connected 

 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 appro- 

 priate 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 



