RELATIONS OF THE DEVONIAN AND CARBONIFER- 

 OUS IN THE UPPER MISSISSIPPI VALLEY.* 



Charles R. Keyes. 



Notwithstundino; the fact that the Devonian and Carbon- 

 iferons rocks of the Upper Mississippi Valley were brought 

 prominently into public notice more than half a century ago, the 

 exact line of demarcation between them has remained one of 

 the mooted points in the stratigraphy of the region. To most 

 of the formations which go to make up the two systems a 

 definite geological age has been, without much doubt, cor- 

 rectly assigned. That regarding any portion of the succession 

 there should arise any material differences of opinion is per- 

 haps somewhat surprising, especially when it is remembered 

 that the general stratigraphical arrangement is not particu- 

 larly complicated. Nevertheless, it is a fact that there is a 

 zone the exact geological age of which has long been in doubt 

 and concerning which little has been done towards the final 

 settlement of its real position. 



The fact that the correlations have been various, and, as 

 late work has clearly shown, in large part erroneous, must be 

 ascribed mainly to insufficient data, since nowhere have inves- 

 tigations been detailed enough to enable the critical evidence to 

 be formulated. The beds of the uncertain zone have been placed 

 first in one system and then in the other, sometimes with a loss of 

 some of its layers in the process of shifting, sometimes with a 

 gain of others. These strata of indeterminate age may be re- 

 garded as including all those lying between the base of the Bur- 

 lington limestone, and those which are commonly put down 

 as the western representatives of the New York Hamilton. 

 Although originally placed in the Carboniferous, these beds 



* Presented in abstract, April 19, 1897. 



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