470 E. O, ULRICH REVISION OF THE PALEOZOIC SYSTEMS • 



frequent uplift is shown by the shaly and locally sandy nature of the 

 liichmondian deposits in Oklahoma, Missouri, Iowa, and Wisconsin. These 

 Eichmondian sediments are in striking contrast to the underlying pure 

 and dolomitic Ordovician limestones. Judging from their characters 

 they suggest finely divided surface wash from old deeply decayed lands 

 sufficiently elevated to permit of gentle denudation. 



The probably wind-blown pure silica sands of the Saint Peter and of 

 the less widely distributed sandstones in the Ozarkian system in the 

 Mississippi Valley indicate large land areas to the north, northeast, and 

 northwest at such times; but these emergences were less in extent and 

 diversity of relief and, excepting the Saint Peter, also of shorter duration 

 than the late Ordovician emergence. Besides, these earlier emergences 

 are scarcely suggested by change to clastic deposition in the Appa- 

 lachian Valley, indicating that western Appalachia was never high during 

 the late Cambrian, the Ozarkian, Canadian, and most of the Ordovician 

 ages. As the deposits in the Appalachian Valley give the fullest known 

 record of Paleozoic events in a single province, it is regarded as the best 

 standard for determining the extent and time values of the submergences 

 and emergences on which the proposed revision of the Paleozoic systems 

 is based. Where defective, the Appalachian record is pieced out from other 

 regions, as the Cambrian, which is better developed in the Cordilleran 

 basin, the earliest Ordovician, which is more fully represented in the 

 Arbuckle uplift in Oklahoma, and the middle Silurian, which is much 

 better recorded in New York, Tennessee, Indiana, and Wisconsin. Yet 

 other parts of the stratigraphic column are more completely represented 

 elsewhere than in the Appalachian Valley, as the lower Devonian in 

 Gaspe, the middle and upper Devonian, the Mississippian, and the Penn- 

 sylvanian in the Cordilleran basin, but these sections are at present less 

 satisfactory than the Appalachian, because the movements and cor- 

 responding brea,ks in the sedimentation are either less clearly indicated or 

 the exposures have not been studied with sufficient regard to stratigraphic 

 details. 



NEOPALEOZOIC DIA8TR0PHIC PERIODS 



The depositional history of the next era, though similar to that of the 

 Eopaleozoic, is complicated by the greater proportion of clastic matter 

 contained in the middle systems (Devonian and Waver lyan). This 

 may be explained, according to the theory of inland migration of the 

 belt of folding (see pages 435 to 442), by assuming increasing elevation 

 of lands contributing to the Appalachian Valley and to areas elsewhere 

 that are similarly located with respect to the margins of the continents. 



