84 ENVIRONMENT OF VERTEBRATE LIFE, ETC. 



and uniform. In general there was a long-continued subsidence of the region, 

 broken by periods of stability and with, perhaps, relative uplift of adjacent land 

 areas during several intervals. The uniformity of the subsidence is shown by 

 the persistence in thickness, areal extent, and character of most of the members 

 of most of the formations. The periods of stability culminated in the formation 

 of the widespread coal beds, after sedimentation had filled the sea and caused its 

 withdrawal, and ended when a renewal of subsidence again let in the saline waters, 

 killing the coal plants. 



"The relative uplift of neighboring land areas is indicated by the periodic 

 recurrence of irregular deposition and a comparatively large proportion of arena- 

 ceous sediments. In most Pennsylvanian formations the strata are remarkably 

 persistent and regular, but in the Pleasanton, Douglas, and part of the Cher- 

 okee formations, and in the Lane, Severy, Scranton, and a few other members, 

 the strata are variable. An influx of sands was usually caused, probably, by 

 changes in the currents of the shallow sea, in the direction of drainage lines on 

 neighboring land-masses, or in the derivation of sediments. During the Pleas- 

 anton and Douglas epochs, however, the phenomena were somewhat more com- 

 plex. As stated more fully on previous pages, there is evidence that the sea may 

 have withdrawn from all or part of Missouri in both Pleasanton and Lawrence 

 time, while long and rather deep channels were formed by subaerial erosion. 

 These changes appear to have been effected by slight tilting and folding in 

 northern and western Missouri, as well as by differential uplift of the Ozark region. 



"After the close of the Pennsylvanian there were two periods of folding. 

 The first of these resulted in the blocking-out of the main broad features of the 

 present structure, namely, the monoclinal dip to the west in north Missouri and 

 to the northwest in the west-central part of the State. The second period of 

 folding caused the formation of narrow and comparatively sharp anticlines and 

 associated synclines trending northwest-southeast and markedly parallel through- 

 out the State. * * *" 



