IOWA ACADEMY OF SCIENCES. 107 



regard them as applying widely, if not universally. For 

 many years general correlations have been carried on 

 almost entirely by the biotic methods. At the present 

 time they predominate overall others, and are, in fact, the 

 foundation of our commonly accepted system of geological 

 synchrony. 



It is beginning to be recognized more and more clearly 

 that organic remains are not the all-deciding factors in 

 questions of correlation; that they are, in reality, merely 

 accidental characters, and that when depended upon they 

 must always be, and are in fact, taken in connection with 

 physical features. 



In the Mississippi valley not nearly enough detailed 

 work has yet been done on the fossils to enable exact cor- 

 relations to be made through the faunas alone. Were it 

 not for the adoption of other and independent methods of 

 correlation, the strata of the region, so far as the parallel- 

 ing of the different vertical sections is concerned, might 

 for a long time remain in a very unsatisfactory condition. 



In the correlation of these strata five distinct methods 

 have been made use of. In consequence, the results 

 obtained by one method have been checked by those 

 arrived at through other independent data. In this way, 

 marked discrepancies in the readings of one set of records 

 have been detected and corrected. The values of the sev- 

 eral methods have been quite different in different locali- 

 ties, but when all could be applied in a single district the 

 comparative results have been full of interest. This has 

 been particularly notable in the case of northeast Mis- 

 souri, in the area occupied by the original Kinderhook. 



In order of their practical values in the field work in 

 this district these five methods are similarly of lithologic 

 sequence, lithologic similarity, faunal comparison, orotaxis, 

 and homogeny. 



