512 E. O. ULRICH REVISION OF THE PALEOZOIC SYSTEMS 



Eden shale and the lower 50 to 100 feet of the Fairview limestone before 

 the upper beds of the latter, in which the fanna is most like that of the 

 Catheys, are reached. A still greater value for the interval is suggested 

 by sections in the Appalachian Valley, where it sufficed for the deposition 

 of nearly 1,500 feet of calcareous shale and sandstone. A third example 

 is found in the Spergen and middle Sainte Genevieve (Fredonia) oolites, 

 which contain very similar faunas and are in contact on Monte Sano, 

 near Huntsville, Alabama, but separated by approximately 400 feet of 

 Saint Louis and lower Sainte Genevieve limestones in the Mississippi 

 Valley below Saint Louis. In all three of these cases it is to be further 

 observed that the intercalated beds do not fully account for the strati- 

 graphic break so slightly indicated by the fossils, since even where the 

 intervening beds are thickest there is still evidence of discontinuity of 

 sedimentation at their bases, and perhaps also at the top. 



(7) Barriers prohibiting intermingling of distinct faunas. — The mere 

 fact that marine faunas in adjacent areas, whether in lithologically similar 

 or dissimilar strata, are totally distinct is not of itself conclusive evidence 

 of great difference in age. Such differences may be due to various kinds 

 of barriers prohibiting intermingling of faunas invading continental seas 

 from distinct oceanic basins, or possibly to currents of varying tempera- 

 tures. Instances of such conditions are suggested in many parts of the 

 country, notably in the Appalachian Valley, where certain nearly con- 

 temporaneous faunas like those of the Levis shales and of some corre- 

 sponding limestone of the Beekmantown, and those of the Normanskill 

 and Athens shales and of limestones of Upper Chazy age, had a parallel 

 but perfectly distinct distribution extending for hundreds of miles. These 

 instances of nearly contemporaneous faunas in lithologically dissimilar 

 beds can not be explained by ascribing them to normal differences in 

 habitat within a continuous sea. The character of the respective faunas 

 is fatal to that explanation, since the more littoral faunas occur on the 

 west side, while the graptolite faunas, which the best authorities regard 

 as essentially pelagic in habitat, are found between them and Appalachia 

 and Taconia, the areas of relatively high land during the Eopaleozoic era. 



N"ot to be misunderstood, it should be said of these examples that 

 neither the Levis nor the Normanskill-Athens zone is believed to be 

 strictly contemporaneous with a limestone formation a few miles to the 

 west. On the contrary, I am of the opinion that these graptolite-bearing 

 shales were deposited at times when the limestone areas were in a state 

 of emergence, and that when the latter were again submerged the Levis 

 and Athens troughs were in part or whole emerged. 



