Central Iowa Section of the 3Iiss. Series. — Bain. 321 
In southeastern Iowa Gordon,* in stud3nngthe Saint Louis, 
has found it to be divided into three members: 
(1) Gray, compact, and granular limestone. 
(2) Brccciated limestone. 
(3) Arenaceo-magnesian limestone beds. 
These three divisions correspond well with the beds of cen- 
tral Iowa and, while the two sections have not asA^etbeen def- 
initely correlated by detailed stratigraphic work, there can 
be little doubt of their equivalenc}'. 
Augusta Formation. 
The rocks now grouped under this name were long known 
and studied in southeastern Iowa and neigiiboring regions un- 
der the names Keokuk and Burlington limestones. Recently 
it has been shown that these two are in reality one formation 
both stratigraphically and paleontologically. It is interest- 
ing to note that this is in strict accord with the facts as ob- 
served in central Iowa. Indeed, if the work on these rocks 
had begun here rather than in their type localit}^ it is doubt- 
ful if the formation would ever have been divided. The lith- 
ological and faunal characteristics of the different exposures 
throughout Washington and Keokuk counties are almost iden- 
tical. There is throughout the same coarsely sub-cr3'stalline 
dark gray or drab to white limestone, showing streaks oxi- 
dized brown ; the same irregular layers of chert; the same clay 
partings and other features of identity. This is not due to 
the fact that only a portion of the formation is exposed, for 
the outcrops show the entire thickness from the base of the 
Saint Louis to the top of the Kinderhook. There is through- 
out a considerable uniformity of material. The arenaceous 
layers which appear in Louisa county seem to be entirely ab- 
sent. Everywhere there are indications of stable conditions 
and a corresponding uniformity of faunal features is noticed. 
Only occasionally is a form usually considered as distinctive- 
ly Keokuk, such as Spirifer hxjaniWixW, or as characteristic- 
ally Burlington as Spirifer grime.si Hall, found. Tlie larger 
number of fossils found might be labeled indiscriminately 
from any one of the exposures. 
In Washington county this formation underlies a broad belt 
running through the central part of the county. The princi- 
*Geol. of Van I'uren county, not yet i)ublislied. 
