STRATIGRAPHIC TAXOKOMY 607 



are inferior in geographic extent to the corresponding Ordovician de- 

 posits, and so we should not be surprised when it appears that the 

 Waverlyan presents no marine sediments in southeastern North America 

 corresponding to the Cincinnatian, The average altitude having, accord- 

 ing to theory, grown greater in the Tennessean, the initial (Warsaw) 

 submergence of this period may well correspond to the oscillating Black 

 Eiver stage in the Ordovician. Under this interpretation, the Tennes- 

 sean has no accessible deposits comparable to the Saint Peter and 

 Chazyan, while the Chester formations would correspond to the Trenton 

 and possibly early Cincinnatian. 



The remaining Paleozoic systems, namely, the Ozarkian, Devonian, 

 and Pennsylvanian, likewise seem to have begun with sedimentary stages, 

 indicating considerable preceding warping. In each of these periods, 

 accessible deposition in continental basins was delayed to at least the 

 second or Stones Eiver stage of the Ordovician sequence. In other words 

 the continental creep subsidence corresponding to the "Saint Peter^^ 

 invasion in the Ordovician and the Eichmondian in the Silurian, did not 

 reach the level at which the Mississippi Valley north of Saint Louis 

 would be submerged. Evidently, the average altitude of the continent 

 during each of these periods was greater than in the Ordovician and 

 Silurian. The Same conclusion is suggested already by comparing the 

 maximum extent of the continental seas in each of the Paleozoic periods. 



The probable truth of deductions based on these comparisons, is in- 

 dicated by the fact that whereas the middle Devonian seas spread much 

 more extensively over the median areas of l^orth America than did the 

 others, save the Ordovician and Silurian, the first or Helderbergian 

 series of the Devonian extends northward in the Mississippi Valley to 

 Perry County, Missouri. Depending on the facts in hand, it is inferred 

 that the inaccessibly recorded intervals between the Canadian and the 

 Ordovician and between the Ordovician and the Silurian are shorter than 

 those separating the Cambrian and Ozarkian, the Ozarkian and Canadian, 

 the Silurian and Devonian, and the last from the Waverlyan, and, 

 further, that the interval in all these cases is much shorter than those 

 between the Waverlyan and the Tennessean, and the Tennessean and 

 Pennsylvanian. Ehythmic relationship between these supposedly long 

 and short intervals is suggested, but more stud}^ is required before any- 

 thing of the kind may be said to have been established. Whatever the 

 issue of such studies the great incompleteness of the known stratigraphic 

 record is assured beyond dispute; and it is no less certain that attempts 

 to estimate the length of geologic time, which do not take these unre- 

 corded intervals into account must inevitably fall far short of the truth. 



