172 THE DEVONIAN AND CARBONIFEROUS. [bull. 80. 



the characteristics of species coordinate with temporal sequence. It is 

 the light which evolution has thrown upon the history of organisms 

 that is doing more to clear up the correlations involved than all the 

 minute stratigraphy which has been applied to their interpretation. 

 The true position of the fauna in the chronologic scale was, moreover, 

 first clearly discerned in the Mississippian series by Meek and Worthen, 

 who, in 1861, proposed the name "Kinderhook group" for the errone- 

 ously identified Chemung rocks of Iowa, Illinois, and Missouri. The 

 fundamental correlation involved had been announced as early as 1847 

 by M. de Yerneuil, but Mr. Meek was the first Americau palaeontologist 

 to insist on the correctness of the interpretation, and to carry it out in 

 the classification of the rocks of the country. 



Another problem which chiefly concerns the various members of the 

 Mississippian series is that regarding the subdivision and correlation of 

 the parts of the series as exhibited in separate sections. 



So far little advance has been made beyond the interpretation given 

 by Dr. D. D. Owen in 1852, chiefly on structural grounds. 



In the geological reports of Iowa and Illinois, and in separate publi- 

 cations elsewhere, the faunas have been largely described, but the 

 materials have not been studied with sufficient attention to their biologi- 

 cal character to determine the true relations of the faunas to each 

 other and to chronologic sequence. The evidence now in hand enables 

 us to point out where to draw the paleontologic lines to indicate the 

 three general faunas above named, 1, Chouteau; 2, Osage group; and 3, 

 Genevieve group ; but the full content of each fauna and the precise 

 points at which the stratigraphic lines should be drawn in local sections 

 is not in all cases clear. 



