Handbook of Paleontology 419 



valley; the name Pennsylvanian (H. S. Williams, '91) 

 from the marked development in the Pennsylvanian area. 

 In Europe the terms Lower and Upper Carboniferous 

 continue to be largely used for the two systems. The 

 name Permian was proposed by Murchison (1841) from 

 the Russian Gouvernement of Perm where beds of this 

 age were found extensively. The "Carboniferous" sys- 

 tems together constitute about one-tenth (9 per cent of 

 geologic time). 



Geology. The Mississippian system is set off from 

 the Devonian below by a complete break due to the 

 marked retreat of the seas at the end of that period. 

 Submergence started again in early Mississippian or 

 Waverlyan time and reached its maximum extent toward 

 the latter part of the Waverlyan. At the close of Waver- 

 lyan time there was a widespread withdrawal and marked 

 change in seaways. The seas of late Mississippian (Ten- 

 nessean) began a renewed spread, reaching their maxi- 

 mum about the middle of this time, though the continen- 

 tal seas were never as extensive as in early Mississippian 

 times. The land area of Appalachia still existed. The 

 deposits in the Appalachian trough were derived from 

 this land area and consisted for the most part of coarse 

 sands and muds, marked with sun cracks, ripple marks 

 etc. that indicate an arid or semi-arid climate. In the 

 Acadian province was another basin in which wholly con- 

 tinental deposits were laid down in early Mississippian. 

 In late Mississippian time conglomerates, sands and muds 

 were deposited in seaways, the presence of gypsiferous 

 beds indicating that bodies of sea water were occasionally 

 shut off. During the Mississippian the interior sea ex- 

 panded widely and probably covered nearly the whole 



