552 E. O. ULRICH REVISION OF THE PALEOZOIC SYSTEMS 



posits ( Phyllograptus bed) in northern Arkansas to the formations of 

 the same period in central Pennsylvania. 



At Bellefonte, Pennsylvania, the greatest known development of 

 Canadian limestones is excellently exposed. The four formations, named 

 from below upwards the Stonehenge limestone, the Nittany dolomite, the 

 Axeman limestone, and the Belief onte dolomite, into which the Canadian 

 is here divisible, have an aggregate thickness of over 4,200 feet. The 

 lowest of these, a nearly pure limestone, rests on the Kittatinny forma- 

 tion, which is determined on stratigraphic and fannal evidence to be 

 early Ozarkian in age. The sequence, therefore, is incomplete, middle 

 and upper Ozarkian deposits being absent. Traced southward along 

 the strike, a part of the missing beds is found. South of Eoaring Spring, 

 namely, where the Kittatinny is more fully exposed, a thick northwardly 

 overlapping wedge of middle Ozarkian chert is intercalated between the 

 Kittatinny and the base of the Canadian formations. 



In the further pursuit of the inquiry we are obliged to resort to other 

 criteria usually employed in correlating formations. Eelying chiefly on 

 fossil evidence, we know that the Chepultepec zone of the Alabama 

 Ozarkian section is represented at the top of the Little Falls dolomite in 

 New York, and that this zone is there separated by an unconformity from 

 the Tribes Hill limestone, which is correlated on good fauna! grounds 

 with the Stonehenge formation at Belief onte (Ulrich and Cushing, 

 1910). The persistence of the unconformity at the base of the Stone- 

 henge-Tribes Hill zone proves complete emergence of the Appalachian 

 Valley at the close of the Chepultepec, which is the last of the Ozarkian 

 deposits therein laid down. 



The completion of the chain of evidence on which continent-wide 

 emergence during an Ozarko-Canadian interval may be fairly inferred 

 requires only that it be shown that the highest known Ozarkian — the 

 Jefferson City dolomite of the Missouri section — is not of the age of the 

 Stonehenge and Tribes Hill limestones, but that it belongs in the hiatus 

 between these limestones and the Chepultepec zone. 



Unfortunately, so far as known, all three of these zones are nowhere 

 superposed. We do know, however, that the Jefferson City is younger 

 than the Chepultepec, the fauna of the latter being under the Jefferson 

 City, in Missouri. We know, also, that in northern Arkansas the 

 Jefferson City is separated by an unconformity from the overlying Yell- 

 ville Canadian ; but the exact position of the lowest Yellville zone in the 

 Canadian section of central Pennsylvania has not been fully established. 

 The Ozarkian affinities of the Yellville fauna suggest that the formation 

 is early Canadian in age, but as both invaded from the south this re- 



