498 GEOLOGY. 



great division of the old Carboniferous period, and has been variously 

 designated Carboniferous, Coal Measures, Upper Carboniferous, and 

 Pennsylvanian. West of the Great Plains this second division was, 

 like the first, a time of wide-spread submergence. 



(3) The third division of the period, as formerly defined, was 

 characterized by a notable deformative movement, which resulted, 

 toward the close of the period, in the folding of the Appalachian moun- 

 tains, and less pronounced deformations elsewhere. During the earlier 

 part of this movement the record shows merely a general withdrawal of 

 the sea. Lakes (some of them salt) and partially enclosed seas were 

 developed at various points where the open sea had been. Nearly 

 the entire top of the true continental platform seems to have emerged 

 by the close of the period, and to have suffered more deformation than 

 had occurred at any time since the beginning of the Cambrian period. 

 This division of time is known as the Permian. 



The general relations of land and water in the middle latitudes 

 of the eastern part of the continent during the three divisions of time 

 mentioned above may be roughly illustrated by Fig. 229. 



There has long been doubt as to the propriety of regarding the 

 Permian as a part of the Carboniferous, and though mentioned in this 



M C P 



: . -..-"t ' ■■ — — *■■ — - ii - - -.■ — ■■ «■■■. - ..i | * »T-ifc ■ - — ■» - « i r . T , ---n| 



Fig. 229. — Diagram illustrating the general attitude of the middle latitudes of the 

 eastern part of the United States, with reference to sea-level, during the Mississippian 

 Pennsylvanian, and Permian periods. The dotted line represents land, the full 

 line, sea level. 



connection, it is here regarded as a separate period, coordinate with 

 the Silurian, Devonian, etc. 



There seem to be sufficient reasons, also, for regarding the Missis- 

 sippian or Early Carboniferous formations as a system coordinate 

 with the Silurian, Devonian, etc., and this classification is here adopted. 

 The reasons for this departure from the current classification will be 

 indicated after the history of the period has been sketched. 



