129 



The thickness of the Jeffersonville limestone in Indiana 

 is very much less than either that of the Grand Tower forma- 

 tion in Illinois, or of the Onondaga limestone in New York. 

 Moreover, it is in New York and in Illinois that the transition 

 from the Oriskany to the Onondaga is complete, no trace of 

 Oriskany strata occurring in Indiana. 



From the foregoing table, it may be seen that all of the 

 identified species of fossils of the Grand Tower formation 

 that occur also in the Jefifersonville beds of Indiana appear in 

 the Grand Towner section above the base of the horizon S. 56 

 h (about the middle part). A number of the Jefifersonville 

 species appear below that horizon, but all of these are forms 

 that have a considerable vertical range and are present also 

 in the beds above S. 56 h, as shown in columns 1 and 2 of the 

 table. With the exception of the single species, Odontocephalus 

 aegeria, that appears for the last time in S 56 h, not a single 

 one of the diagnostic fossils of the low^er 75 feet (practically 

 the lower half) of the Grand Tower strata, occurs in the 

 Jefifersonville limestone of Indiana. From these facts it is con- 

 cluded that no strata corresponding with the lower half of 

 the Grand Tower formation are present in Indiana ; and that 

 the Jefifersonville limestone represents deposition during only 

 the latter half of Onondaga time. 



Evidence Bearing on the Source of the Onondaga Fauna. 

 Concerning the origin of the Onondaga fauna, Weller^ has 

 suggested that, "From the geographic distribution, it may 

 have originated somewhere in the Arctic regions ; and that 

 representatives of it migrated southward, both into North 

 America and into Europe. The typical Niagaran fauna, 

 as it is found in the Appalachian province, is thought to have 

 come into the region from the north through the junction of 

 the Hudson's Bay basin with the interior basin, and, when it 

 withdrew from the interior, it doubtless followed the same 

 route by which it had entered. During the period of read- 

 justment between Silurian and Devonian time it is not im- 



1 Weller. Journal of Geology. Vol. X, p. 429. 1902. 



