576 SAMUEL CALVIN 



The Lower Carhonijerous-Mississippian. — It is possible, indeed 

 probable, that there is an unconformity between the Devonian and 

 Lower Carboniferous, but it has not been positively demonstrated. 

 The actual contact of Devonian and Kinderhook has not been 

 observed. The faunal break is not exceptionally great. The stro- 

 matopores, favosites, and most of the other corals characteristic 

 of the Devonian do not appear in the Kinderhook, and the same is 

 true of the Stropheodontas, Strophonellas, and Atrypas; but the 

 Orthothetes, Rhipidomellas, Spirifers, and Cyrtinas have pronounced 

 Devonian relationships. Productella pyxidata and Ptyctodus cal- 

 ceolus, collected in the Kinderhook of Missouri, furnish other points 

 of affinity between the Kinderhook and Devonian faunas. On the 

 other hand, leaving out Productella, the Productidae of the Kinder- 

 hook are decidedly Carboniferous, and the fish fauna in general 

 points unmistakably in the same direction. The Burlington lime- 

 stone and the Keokuk limestones of the earlier geologists of Iowa 

 and Illinois have been united under the term '' Osage " or " Augusta. '^ 

 While the two alternative names are not quite synonymous, it is 

 probable that geologists will unite on the term "Osage" for the 

 assemblage of limestones, cherts, and shales under consideration. 

 The St. Louis limestone brings the Iowa Mississippian to a close, 

 and this formation remains as originally defined. When the later 

 Mississippian, the Kaskaskia or Chester, was deposited, the shore 

 lines, so far as now known, lay outside the limits of our state. That 

 the greater part of the Mississippian was characterized by compara- 

 tively arid climate is supported by many lines of evidence. 



The Pennsylvania series includes the productive coal-measures, 

 and presents the usual characteristics, biologic and lithologic, of 

 equivalent deposits in other parts of the world. One of the most 

 pronounced unconformities in the Mississippi valley occurs between 

 the Upper Carboniferous and the older formations. When the 

 Pennsylvanian series began, the shore-fine was probably as far 

 south as Arkansas. There are indications that, at that time, Iowa, 

 stood higher with respect to tide level than it does at present,' and 

 deep erosion trenches were cut in the Silurian, Devonian, and Lower 

 Carboniferous formations. When subsidence allowed the sea to 

 return, it advanced upon a scarred and eroded surface, depositing 



