STRATIGRAPHIC CLASSIFICATION DIASTROPHIC CRITERIA 429 



flank of the jSTashville dome of at least two formations, one being the 

 Lowville, the other comprising the pre-Catheys part of the Cannon 

 limestone. 



Having proved progressive overlap for three of the Ordovician forma- 

 tions concerned in the process of alternate tilting of the domes of the 

 Cincinnati geanticline, and as the present knowledge of the associated 

 formations is merely inadequate on this point, I regard myself as justified 

 in assuming that, at least as a rule, reverse tilting was deferred till after 

 the close of each stage. The sharp break between the overlapping forma- 

 tions Justifies the inference that sea withdrawal then occurred rather 

 generally about these uplifts. Finally, the trend of the evidence strongly 

 suggests that the reversal of the preceding attitude took place during 

 these increased emergence intervals, so that when the waters again ad- 

 vanced they submerged areas on the opposite flanks of the uplifts that 

 had not been covered in the depositional stage immediately preceding. 



Except in the cases of the great north-south tilts, which involved the 

 whole length of the continent, it is not contended that in these interforma- 

 tional emergences the waters were always completely withdrawn from the 

 regions surrounding the domed areas of frequent emergence. In fact, 

 complete withdrawal probably occurred only at times, marking the close 

 of periods, epochs, and stages, while in the intervals separating the smaller 

 formations the waters are thought to have retreated only as far as the 

 deeper parts of the adjacent major downwarps. That the latter contain a 

 more complete sedimentary record than is found in the exposed sections 

 on the flanks of the uplifts seems scarcely open to serious contradiction — 

 certainly not in the case of overlapping formations that may be traced 

 by long outcrops or through records of deep wells, away from the summit 

 of a structural dome and that may thus be shown to add more and more 

 beds to their bases. Often the increase in thickness is rapid, as in the 

 case of the Kimmswick limestone, which thickens from 40 feet at its 

 outcrop, 20 miles west of St. Louis, to about 100 feet in the Belcher well 

 within the city, and to nearly 200 feet in the Monks Mound well, 5 miles 

 east of Mississippi Eiver. That this buried record may often be of very 

 considerable importance is indicated by such thin formations as the cherty 

 Flanagan limestone, which does not exceed 40 feet, and is usually much 

 less, in central Kentucky, while the corresponding part of the strati- 

 graphic record in the northeastern quarter of the rim of middle Tennessee 

 comprises a maximum thickness of something like 175 feet of solid lime- 

 stone. In Tennessee it forms the greater, middle, part of the Cannon 

 limestone, a formation that thins rapidly to the west and finally wedges 



