DIASTROPHISM AND THE FORMATIVE PROCESSES 333 



earth's history in so many parts of the globe. But at the close of 

 the period there was a widespread withdrawal of the sea. In North 

 America the seas retired from a large part of the United States, 

 New Brunswick, and Nova Scotia, to such an extent that when the 

 sea again advanced in the Pennsylvanian or Upper Carboniferous 

 period, the new sediments were laid down unconformably upon 

 the eroded Mississippian beds over wide areas. This unconformity 

 at the top of the Mississippian, or at the base of the Millstone Grit, 

 is continued very widely throughout most of the interior and western 

 states and an unconformity at about this same horizon appears also 

 at various points in Alaska.^ It was chiefly because of the uncon- 

 formity which occurs at this horizon over such wide areas, not only 

 in North America, but in other continents as well, that the portion 

 of the Carboniferous below the unconformity was urged as a sepa- 

 rate period under the name Mississippian. 



Distinct folding movements occurred in the Arbuckle region 

 of Oklahoma. Near the close of the Mississippian or beginning 

 of the Pennsylvanian, the rocks of the Arbuckle region were folded 

 and the western part thrown into mountains. Faulting also 

 occurred on a large scale.^ As a result of the elevation of these 

 mountains at this time, with the attendant acceleration of erosion 

 and rapid clastic sedimentation, the sediments of the succeeding 

 Pennsylvanian period have reached a thickness in the adjacent 

 portion of Arkansas of 18,000 feet.^ These Arkansas Coal Measures 

 correspond to only a lower part of the Pennsylvanian."* 



In Europe conditions were somewhat similar. De Lapparent 

 states that there was considerable volcanic activity from the 

 Armorican region to the Vosges together with a complete with- 

 drawal of the sea from the region, at the close of the Dinantian, or 

 Lower Carboniferous. At this time there was energetic folding 

 in the Vosges on the eastern frontier of France, while evidences of 



I A. H. Brooks and E. M. Kindle, "The Paleozoic Section of the Upper Yukon, 

 Alaska," Science, XXV (1907), 182. 



= J. A. Taff, "Geology of the Arbuckle and Wichita Mountains in Indian Terri- 

 tory and Oklahoma," Prof. Paper 31, U.S. Geol. Survey (1904), p. 37. 



3T. C. Chamberlin and R. D. Salisbury, Geology, II (1906), 562. 



••A. J. Collier, "The Arkansas Coal Field," Bull. 326, U.S. Geol. Survey (1907), 

 p. 24. . 



