DEVONIAN OUTLIER NEAR ROLLA. 279 



Correlation. — From the foregoing table it is evident that 

 this fauna is of Onondaga age, and that it is the partial equiva- 

 lent of the Grand Tower formation of southern Illinois and south- 

 eastern Missouri. Its affinities are entirely with the eastern 

 Devonian and have no resemblance to the later Devonian faunas 

 of Iowa and north central Missouri. Of the thirty-seven identi- 

 fied forms, seventeen occur in the Grand Tower formation of 

 southern Illinois, thirty in the Jeffersonville beds of southern 

 Indiana, thirteen in the Onondaga group of Michigan, twenty-two 

 in the Onondaga of Ohio and eighteen in the Onondaga of New 

 York. These figures are not exact and are probably too low, for 

 the faunal lists from the various regions are incomplete and 

 represent compilations in most cases. The most complete lists 

 are those from the Grand Tower formation and from the Jeffer- 

 sonville beds. Weller and Savage have shown the relationship 

 of the Grand Tower fauna to the Onondaga of the eastern United 

 States. 



Savage has also shown that the Jeffersonville beds are the 

 equivalent of the upper portion of the Grand Tower of Illinois. 

 Since more than 80 per cent of the forms occurring at Rolla are 

 also found in the Jeffersonville beds, it seems certain that this 

 outlier belongs to the upper portion of the Grand Tower forma- 

 tion. Certain horizons in this formation are reported to be full 

 of corals, but until the faunal lists for this formation are com- 

 pleted, a closer correlation cannot be made. 



Conclusions. — The presence of a Grand Tower outlier at 

 Rolla indicates a much greater submergence of the Ozark upl'ft 

 during Onondaga time than has commonly been supposed. The 

 nearest outcrops of the Grand Tower formation are at least 100 

 miles to the east. The St. Francois Mountains, the structural 

 center of the uplift, are directly between the two exposures, and 

 it is not believed that these were covered in Devonian time. 

 In view of the thinning out of the Devonian to the north, it may 

 be assumed that the Onondaga sea extended westward along the 

 southern border of the St. Francois Mountains, and that it may 

 have covered much of the southern portion of the uplift. Further 

 field work may reveal other outliers, which will enable the 

 boundaries of this sea to be traced more definitely. 



