IOWA ACADEMY OF SCIENCES. 125 



essentially the Augusta formation of Missouri, and are 

 continuous with that formation as developed in the south- 

 western part of the last mentioned state. The widely 

 recognized Batesville sandstone has been proved by Weller* 

 without much doubt, to be the equivalent of the Aux Vases 

 sandstone of the Mississippi river region, the basal member 

 of the Kaskaskia formation. 



It is now generally agreed that the Boston group of 

 northwestern Arkansas is the equivalent of the Kaskaskia 

 limestone and Chester shales of the Mississippi river. 

 Typical Kaskaskia fossils have been found in the shales 

 of this group in the extreme northwestern corner of the 

 state,* and in the adjoining parts of Missouri. 



The exact line of demarkation between the Lower Car- 

 boniferous and the coal measures has not been drawn in 

 Arkansas. In the northwestern part of the state Sim- 

 monds,* without giving any reasons or data for deducing 

 his conclusions, had regarded a thin shaly limestone 

 (called the Kessler) lying about 78 feet above the Pentrem- 

 ital limestone as the topmost member of the Mississip- 

 pian. As the shales beneath the Kessler limestone carry 

 thin coal seams with an abundant flora it may be that 

 these as well as the Kessler may eventually prove to 

 belong more properly with the coal measures. 



At present it is uncertain just where the separating line 

 between the Mississippian and coal measures should be 

 placed. In the Boston mountains, the stratigraphic suc- 

 cession is apparently unbroken from the Boone cherts 

 (Augusta) upwards. Above the Batesville sandstone the 

 undoubted Kaskaskian beds upwards assume more and 

 more the character of coal measures. Into the latter the 

 former appear to gradually merge. No evidence of uncon- 

 formable relationships is anywhere noted in this region. 

 Nor do any of the Arkansas geologists mention any facts 

 indicating that a stratigraphic break might exist. 



The zone of uncertain age is, however, thin; and the 



♦Trans. New York Acad. Sci., Vol. XVI, p. 251, 1897. 



* American Geologist, Vol. XVI, pp. 86-gi, 1895. 



* Arkansas Geol. Sur. , Ann. Rept 1888, Vol. IV, p 109, if 



