THE CAUBONIFEROOS. 107 



sissippi, but \v(M<' f()iii.(><l by the incessant action of llic Pncific waves on shores tliat 

 perhaps for hundreds of miles succiunbed to their po\v<'r, and by broad and rapid rivers 

 which flowed iroiu the mountains and tinon^li the fertile valleys of a i>riineval Atlantis. 



In tlie sea of the Potsdam tliero was an abundance of life, thoiif^li of 

 a low order, huge sea-weeds and delicate brachiopod shells with trilobites 

 of small size. 



The following- list g-ives the names of the genera and species which 

 have been recognized or described by Professor Whitfield : 



Palceochorda prima. Linguhpis Ddkotcnsis 



Pal(eophjcus occidentalis. Oholus ? pedenoides. 



Palceophjcvs . Obolella polita. 



ScoUthus . Obolella nana. 



Lingulepis pinnaformis. Crepicephalus centralis. 



Lingidepis cimeolus. Crepicephalus x^lanus. 

 Lingulepis peraUemiatus. 



SECTION V. 

 THE CARBONIFEROTJS. 



East of the Plains the Carboniferous system is divided into two well- 

 marked series. The lower, known as the Sub-Carboniferous, is character- 

 ized by sandstones and limestones, the former predominating in the neigh- 

 borhood of the Appalachians and the latter in the IVtississippi Valley. The 

 upper, known as the Coal Measures, is marked by alternations of sand- 

 stones and shales, with some limestone and some iron ore, and contains 

 those stores of mineral fuel which have justly given name to the whole 

 system. It Avas thought at one time that a third division had been recog- 

 nized in the Mississippi Valley — a division overlying the Coal Measures 

 and corresponding to the Permian of European chronology — but the line 

 of separation from the Coal Measures proved so shadowy that the attempt 

 to draw it was abandoned. The division is practically ignored at the 

 present time, although it is not questioned that a fauna allied to the Per- 

 mian fauna of Europe finds place at the top of the series and is gradually 

 merged with the Coal Measure fauna below. 



