Cxl CORRELATION OF MARYLAND MIOCEXE 



nated the environment. Since the modification of faunas not interfered 

 with by catastrophic changes of temperature and environment must 

 always be gradual, the exact limitation of the different series of which 

 the Tertiary is made up has of late been expressed in terms of dynamic 

 changes to which the terrains concerned have been subjected. The 

 division of the Tertiary time into two great systems has been generally 

 accepted by geologists. The first, which embraces all the recognized 

 Eocene and nummulitic beds, has been called Eogene, and contains 

 the Eocene and Oligocene series. The second, or Neogene, comprises 

 the remainder of the Tertiar}^, the Miocene and Pliocene series, and 

 was inaugurated and is limited by important dynamic changes in the 

 earth's crust.^ 



According to De Lapparent with the Miocene were ushered in impor- 

 tant changes in the geography and topography of Europe. First in order 

 of importance, as the work of the Miocene period was the elevation of 

 the Alps, or rather of that great zone of elevated plications which, extend- 

 ing from Morocco to Indo-China, the result of successive movements in 

 elevation, forms the southern border of what has been called Eurasia. 

 This immense upheaval was accompanied by the gradual draining of the 

 great lakes which covered much of France and central Europe during the 

 Oligocene, and, isostatically, by the sinking of other parts of the pre- 

 existing land. Following the latter the sea penetrated into the heart 

 of Europe, carrying its fauna with it. Coincidently the denudation of 

 the elevated area gave rise to extended sedimentary deposits radiating 

 from it. Subsequently the communications with the sea were cut off, the 

 eastern basin of the Mediterranean separated from the Atlantic became 

 less saline and the extension of brackishness in the sea to the northward 

 made gradual progress westward, reaching Corsica and the valley of the 

 Ehone, finally becoming in part a series of lakes, around which the great 

 herbivorous mammals of the period found a pasturage. The termina- 

 tion of the Miocene and the beginning of the Pliocene in Europe was 

 marked by a movement in depression of the Mediterranean axis, opening 

 the strait of Gibraltar, giving the Atlantic access to the Mediterranean, 

 where the subtropical members of the marine fauna were replaced by 



1 Cf. De Lappakent, Traite de Geologic, ed. IV, pt. Ill, pp. 1409, 1513, et seq., 1900. 



