MAHYl.AXD GEOLOGICAL SLUVEY 35 



noted the great difference between the fossil and living species, 

 showing that the Medial Tertiary contained but 19 per cent 

 of living forms. He thought that the extermination was 

 due to a fall of temperature. In tlie same and following year he de- 

 scribed many fossils from the Miocene of southern Maryland, and in 

 1842 he correlated his Medial Tertiary with the Crag of England and 

 stated it was Miocene. The boundaries which he gave the ]\Iiocene at 

 that time wore not greatly different from the boundaries which are 

 ascribed (o Ihe Chesapeake Group of to-day. In 18-14, Eogers assigned 

 the diatomaceous earth to a position near tlK3 base of the Miocene. 



About this time much interest was created in the Miocene problem of 

 Maryland by Sir Charles Lyell. He regarded these deposits as Miocene, 

 and gave at some length his reasons for this opinion. He also stated that 

 the Miocene of ]\Iaryland agreed more closely with the Miocene of Lor- 

 raine and Bordeaux than with the Suffolk Crag. Lonsdale also con- 

 cluded from the corals collected in the Miocene which were submitted 

 to him for examination, that the American deposits were probably 

 ncciiniuhited while the climate was somewhat "superior" to that of the 

 Crag and "perhaps" equal to that of the faluns of Lorraine, but "in- 

 ferior" to that of Bordeaux. In the same year Conrad described and 

 figured many fossils from the Calvert Cliffs. 



No more papers of importance appeared on the Maryland Miocene 

 until 1863, when Dana brought out his first edition of the Manual of 

 Geology. In this A\'ork he took occasion to propose the term " Yorktown 

 epoch " for the period during which the Miocene of the Atlantic coast 

 was deposited. The next paper of significance was published by Heilprin 

 in 18S1, in which he discussed the Miocene at some length, and divided 

 it into an ''Older period" and a "Newer period." The Older period 

 contained the older portion of the Miocene of Maryland; and the Newer 

 period, the later portion. He subdivided the Newer period again into 

 the Patuxent Group and the St. Mary's Group. The next year, the same 

 author revised his classification and divided the Miocene into three 

 groups as follows : the Carolinian or the Upper Atlantic Miocene, in- 

 cluding the Sumpter epoch of Dana; the Virginian or ^fiddle Atlantic 



