OSCILLATORY CriARACTER OF CONTINENTAL SEAS 341 



after the first considerable warping of the period. To illustrate with an 

 example, the Tennessean section would thus seem to contain no strictly 

 marine series corresponding in relative position within the system to the 

 Eichmondian at the base of the Silurian, or to the Helderbergian at the 

 base of the Devonian. On the other hand, the Waverlyan probably con- 

 tains no beds of a date relatively so late in the history of this period as 

 the Cincinnatian in the Ordovician and the Cayugan in the Silurian. 

 The Ordovician system differs radically from all the others, because the 

 stage which corresponds to the Richmondian of the Silurian and the 

 Helderbergian of the Devonian, namely, the Stones Elver, is preceded by 

 an earlier depositional stage — the Saint Peter. Other aspects of this 

 idea are discussed in following sections of this chapter, and more particu- 

 larly in Part III, pages 603 to 608. 



The vertical displacement of the strandline and the relief of conti- 

 nental land-masses — General discussion. — While abundant and reasonably 

 decisive data bearing direct!}^, or by inference, on local and general relief 

 of the continents in past ages are readily procured, it is a much more diffi- 

 cult matter to reach satisfactory conclusions respecting tlie total vertical 

 displacement of the strandline in any given age or period. The hori- 

 zontal extent of the several submergences can be determined to within 

 reasonable limits, and with the advance of detailed knowledge a near ap- 

 proximation of the truth seems attainable. But the horizontal element 

 can bear no uniform proportion to the vertical factor of the displacement. 

 Obviously the geographic extent of a submergence depends as much or 

 more on tlie average relief of the land over which the sea is advancing as 

 on the sum of the rise of the waters on the one hand and the subsidence 

 of the land on the other. Thus, in times characterized by relatively great 

 average reh'ef of interior areas of a continent a given vertical displace- 

 ment of the shoreline would result in less extensive submergence than in 

 periods of lower relief. In other words, the submergence of an unwarped 

 or peneplaned area, as, for instance, the surface over which the Eich- 

 mondian transgressed, required much less of vertical displacement of the 

 strandline than did the warped surface prevailing in the Black Elver 

 and the Niagaran. Obviously, too, with similar rates of movement the 

 sea transgressed the former more rapidlv than the latter. (See ]iao-es 

 305, 367, 405, and 540.) 



During the whole of the Paleozoic the relief of the interior areas of 

 N'orth America, and probably of alh continents, is thought to have been 

 very low. That this was so, at least as a rule in the Paleozoic eras, is con- 

 vincingly indicated by the instances of very slight erosion in long emer- 



