306 O. R. Keyes — Time Values of 



The stratigraphical features considered are summed up in 

 the diagram above. It represents a meridional ideal section 

 across the Carboniferous basin of the Western Interior region. 

 The north and south ends are drawn to scale. The white rep- 

 resents the relative formational development ; and the black 

 the portions now missing. 



The very unequal development of the several series has 

 given rise to a tendency to misconstrue the taxonomic ranks 

 of the formations. For example, the Des Moines series. has 

 been sometimes given a rank subordinate to that of series ; 

 while in the case of the Oklahoman the suggestion has been 

 made to have its rank that of a system. 



If the stratigraphical values of the series be represented 

 according to their relative developments, they appear about 

 as follows : 



Cimarron _ 1 



Oklahoman 2 . 



Missourian 4 



Des Moines 1 



Arkansan 35 



Mississippian ... 5 



In the general geological scheme, which is dual in character, 

 the time ratios are as important as those represented by the 

 stratigraphy. Faunal and floral comparisons of the different 

 sections are not possible at this time because exact information 

 is scant. We have, therefore, to rely upon data derived from 

 all the available sources. Assuming that the time occupied in 

 the formation of the Des Moines series, according to the cor- 

 rected valuation hereafter considered, as unity, the factors 

 tending to modify the accepted values indicated by the thick- 

 ness of the several series may be briefly enumerated. 



The Mississippian series is predominently a limestone forma- 

 tion. Taken alone, its lithological composition would indicate 

 a long time element. As a matter of fact, its formation was 

 probably much more rapid than is usual among limestones. 

 The major member is made up of a crinoidal and shell breccia. 

 The accumulation of its material would thus take place many 

 times faster than the formation of fine-grained, non-fossil if er- 

 ous beds through ordinary precipitation. Another feature 

 indicating that the period during which the Mississippian beds 

 were laid down was not so long as might appear at first glance, 

 is the undoubted oscillation of the sea-floor, which grew quite 

 marked towards the close of the period. In these changes of 

 elevation the uprisings at length predominated over the down- 

 sinkings, finally resulting in the complete emergence of a large 

 part of the province above sea-level, and closing the Mississip- 



