FACTS ON WHICH THE HYPOTHESIS RESTS 289 



In the Owego recurrent zone both Phacops rana and Dalmanites calliteles 

 occur. 



The Van Etten recurrent zone lies entirely below the range of Spirifer 

 disjunctus and other associated species of the Chemung formation. 



On following the sections eastward from the Waverly quadrangle the 

 species of the Chemung farma become scarce, and east of the Chenango 

 Eiver very few species of the typical Chemung fauna have been detected, 

 although they are still abundant in the Chemung rocks to the southeast- 

 ward and southward across Pennsylvania, Maryland, and Virginia. 



Interpretation of the Facts 



shifting of faunas 



These facts have been interpreted as evidence not only of a general 

 shifting of faunas coincident with a rising of the land along the eastern 

 edge of the present continent, but of oscillation of conditions and alter- 

 nate occupation of the area by two sets of faunas coming from opposite 

 directions and temporarily living in abundance in the area of central 

 New York. 



LITHOLOGIC CHANGES NOT SUFFICIENT TO ACCOUNT FOR DIFFERENCES IN 



FAUNAS 



The lithologic changes in the sediments containing the different faunas 

 are not sufficient to account for the change in fauna. In quite a number 

 of sections there is no appreciable difference in lithologic constitution 

 between the strata wdiich for 100 feet thickness have been filled with 

 characteristic Chemung species and the immediately following thin zone 

 of a foot or two, containing scarcely a trace of the Chemung species, but 

 holding in great number species whicli if found by themselves would be 

 undisputed evidence of the Hamilton formation. 



DIFFERENCE IN OCEAN WATERS PRESUMED 



It becomes necessary therefore to suppose that the controlling cause 

 determining the presence of one or other fauna is not the character of 

 the bottom on which the sediments which preserved the fauna were laid. 

 We are thus led to conclude that the character of the ocean water has 

 determined the shifting or migration of the faunas. The conditions to 

 which the faunas were adjusted were evidently those of depth, salinity, 

 or temperature of the waters in which the species lived ; and their change 

 of habitation was occasioned by change in the direction, path, or extent 

 of flow of the oceanic currents. 



