BASES OF CLASSIFICATION. 299 



same. The two together form numbers 10 to 14, inclusive, at Louisiana. 

 The " Keokuk limestone" is numbers 1 and 2 of the Keokuk exposures. 

 number 1 of the Warsaw section, and probably number 1 of the Ste. 

 Genevieve outcrops. The "geode bed" appears as number 3 at Keokuk 

 and number 2 at Warsaw ; the typical ''Warsaw 11 embraces numbers 4 

 to (> of the Keokuk section and numbers 3 to 5 at Warsaw. The "St. 

 Louis limestone " is represented by number 7 at Keokuk, number 6 at 

 Warsaw, all of the St. Louis section, and number 3 at Ste. Genevieve, 

 while number 2 of the same section has been called the Warsaw lime- 

 stone (not typical). The "Ste. Genevieve limestone" of Shumard is 

 number 4 of the Ste. Genevieve-Ste. Mary outcrops. The " Aux Vases 

 sandstone" forms bed number 5 between Ste. Genevieve and Ste. Mary, 

 and underlies number 1 of the Chester section a few miles north of the 

 town. The " Kaskaskia limestone" includes numbers 1 to 4 of the 

 Chester section, and the "Chester shales" numbers 5 to 7 of the same 

 section. The Coal Measures are represented at Keokuk by number 8, at 

 Ste. Genevieve by number 7, and at Chester by number S. 



The great abundance of fossils in all the members of the Mississippian 

 series of the interior basin makes the faunal test perhaps the most impor- 

 tant of all in attempting a rational classification of the rocks of the region. 

 Heretofore the remains of ancient life found in these rocks have been con- 

 sidered either from a purely biological point of view, or, in the majority 

 of cases, from the standpoint of the mere species-maker ; and it is only 

 within the past few years that large numbers of species taken together 

 have been compared with one another in order to marshal the confused 

 collections into orderly arrangement, so that faunas may be studied as a 

 whole. 



The second important consideration to be taken into account in the 

 present connection is the stratigraphical testimony. In the case of the 

 Kaskaskia the physical breaks are unusually prominent, both above and 

 below, over its entire extent in the upper Mississippi valley. What has 

 just been said of the upper member of the series is equally true of the 

 one immediately underlying, though in a less marked degree and over 

 only a part of its superficial occurrence. Between the lower two groups 

 the physical continuity is scarcely broken, and the separation is chiefly 

 upon faunal and lithological grounds. 



Lithologieally the upper two members of the Mississippian are more 

 alike than any of the others: yet as a rule they are readily distinguish- 

 able everywhere. The Osage group of limestones is over all its range 

 encrinital, and stands out in marked contrast from the other three sec- 

 tions ; while the lower subdivision is very different again, both in the 

 calcareous and the argillaceous portions. 



X I. I '.i i i Rkoi Si* \ h., Vol.. ::. 1801. 



