MARYLAND GEOLOGICAL SURVEY Cxliii 



of the series grouped in later American classifications with the upper 

 Oligocene. It has been united by Suess with the Oligocene Aquitanien. 

 Being a matter in which nomenclature rather than geology is concerned 

 its consideration may well be adjourned until a more thorough knowledge 

 of the supposed American equivalents is available. The European 

 characteristics of this stage comprise the earlier part of the period of 

 elevation during wliich the disappearance of the inland lakes and the 

 inception of fluviatile drainage were in progress. 



2. Helve'tien. — This corresponds more exactly to the American defi- 

 nition of the Miocene of Maryland and Virginia, being the period of 

 uplifts and of culmination of the invasion of the southern sea into the 

 resulting isostatic depressions. 



3. ToRTONiEN. — During this period the most extreme elevation of 

 tlie uplifts was attained and with this some diminution of the marine 

 transgression and of the apparent sea-temperatures. It is probable that 

 this stage should be united with the preceding, as it is in a number of 

 cases only indicated by a fades, and barely distinguishable from the 

 Helvetien. It should be noted that the arms of the Mediterranean sea 

 which deposited the marls of the Vienna Basin, the MoUasse of Switzer- 

 land, and the Miocene of Southern France, were inhabited by a fauna 

 derived from the south, and of a subtropical character; hence in no case 

 strictly comparable with a fauna, like that of the American Chesapeake, 

 derived from cool-temperate seas. It is to the fragmentary Miocene of 

 North Germany and Denmark that we should look, if at all, to find the 

 time-analogues of our Chesapeake species. 



4 and 5. Sarmatien and Pontien or Pannonien. — -During these 

 stages, which might well be imited, the Mediterranean sea became sepa- 

 rated from its eastern inland extensions, which gradually lost their 

 salinity and deposited the remarkable Congeria beds and other brackish 

 water sediments or lake beds, with the formation of which European 

 geologists regard their Miocene as having terminated. 



In America, speaking broadly, as stated by Dr. Clark, the Miocene 

 appears at its inception unconformably and suddenly upon the surface 

 of the Eocene which in certain localities it transgresses. In the northern 

 part of its range the Eogene strata seem to have suffered much more 

 from denudation than in the corresponding series at tlie south on the 



