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 Low 7 er 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. 86-91, 1895. 
* Arkansas Geol. Sur. , Ann. Rept 1888, Vol. IV, p. 109, 1888. 
