644 THE JOURNAL OF GEOLOGY. 



relatively little interruption, until the close of Paleozoic time. 

 Certain minor disturbances occurred along the eastern bor- 

 der of the sea, but they were not of sufficient extent to affect 

 a general conclusion — which is, that the depression of the areas 

 of deposition within the continental platform continued without 

 reversal of the subsidence during Paleozoic time. During Cam- 

 brian, and it may be late Algonkian time, the extended interior 

 Mississippian region was practically leveled by denudation, the 

 eroded material being carried into the Cordilleran and Appala- 

 chian seas, and, probably, to a sea to the south. 



The sedimentation of the Mississippian area in Paleozoic time, 

 between the Appalachian and the Cordilleran seas, was small as 

 compared to that which accumulated in the latter. In Devonian 

 time there does not appear to have been any sedimentation in the 

 western portion of it west of the. 94th meridian and east of the 

 Cordilleran sea, and it was slight in the same interval in the 

 Appalachian sea south of the 37th parallel. 1 There is little if 

 any evidence in the sediments of Paleozoic time to show that 

 they were deposited in the deep, open ocean ; on the contrary, 

 they were largely accumulated in partially enclosed seas or 

 mediterraneans and on the borders of the continental plateau. 

 The former is particularly true of the sedimentation of the Cor- 

 dilleran and Appalachian seas and the broad Mississippian sea. 



The close of the prolonged period of Paleozic sedimen- 

 tation was brought about by what Dana has termed the 

 "Appalachian revolution." The topography of the continent 

 was more or less changed, and the conditions of sedimentation 

 that followed were unlike those that preceded. This revolution 

 raised above the sea level a considerable portion of the Cor- 

 dilleran and the Appalachian sea-beds and also of the Mississip- 

 pian sea, east of the 96th meridian and north of the 34th parallel. 



x The non-occurrence of Devonian sediment has not yet been fully explained. It 

 has been suggested that the sea beyond the reach of mechanical sedimentation was too 

 deep for the deposition of calcareous deposits. It is more probable that the sea was 

 shallow and an area of non-deposition, or that its bed was raised to form a low, 

 level land surface at a base level of erosion that was subjected to very slight degrada- 

 tion. 



