130 



probable that the restricted Niagaran fauna became isolated 

 in the Arctic region, and that from the elements of this fauna 

 during a long period of time, the Onondaga fauna was evolved ; 

 and that this modified fauna once more entered the interior 

 basin from the north when the Onondaga seas overspread 

 this region." 



The fact that corals and cephalopods were conspicuous ele- 

 ments of the Niagaran fauna, and that representatives of these 

 classes, changed to be sure from their Silurian ancestors, are 

 important elements in the Onondaga fauna of Ontario, New 

 York, Ohio and Indiana supports this view. The distribution 

 of the fish remains of this time also favor such an origin. 



Schuchert- has suggested that the Onondaga fauna entered 

 the interior basin of North America from the south. He 

 bases his view on the great abundance of corals in the Onon- 

 daga strata of Ohio and Indiana. Since reef building corals 

 of the present are limited to warm seas, he assumes that this 

 is a warm water fauna, and that its source was in southern 

 waters. 



The evidence furnished by the sequence of fossils in the 

 Grand Tower section is interpreted as indicating that the 

 Onondaga fauna reached the interior of North America from 

 two different sources. The fact that deposition was continuous 

 in southern Illinois from the upper Oriskany into the Onon- 

 daga shows that early Onondaga sediments are present in the 

 Illinois region. It is to be noticed that the great Onondaga 

 coral development that occurred in Indiana and Ohio was 

 not present in southwestern Illinois. Some of the character- 

 istic coral species, as Cyathophyllum rugosum and Favosites 

 emmonsi, are not rare in the Grand Tower section, but they ap- 

 pear only in the upper part. The fact that the greater portion 

 of the Grand Tower strata are (|uite jnire limestones shows 

 that it was not the muddy condition of the seas that barred the 

 corals from this region. It is not ])robable either that the 

 greater coldness of the water here was an inliibiting factor. 



It may be seen from the table that a few corals were present 



2 i-chuchert. Bull. Geol. Soc. of America, Vol. XX, p. 491. 



