290 LTE S| OOLINA ER OTN GHOLO GNA 
the study of this formation by the author, in the field work of 
1893, under the auspices of the lowa Geological Survey. 
EARLIER DESCRIPTIONS. 
Owen, 1852.—The first account we have of the geology of 
this region is that of Owen in 1852. While detailed work was 
not attempted, his descriptions give evidence of close and accu- 
rate observation. He divided the Lower Carboniferous into an 
upper and a lower series, and named the various subdivisions 
from lithological or faunal characteristics. No attempt was © 
made to correlate with rocks in other regions of the United 
States, but in accordance with the prevailing usage of that time 
he essayed to establish the equivalency of the divisions of the 
upper series with the members of the Carboniferous section of 
Yorkshire. 
OWEN’S SECTION OF THE LOWER CARBONIFEROUS. 
Upper Series. 
f. Upper concretionary limestone. 
Gritstones. 
Lower concretionary limestone. 
Gritstones. 
Magnesian limestones and shales. 
Geodiferous beds. 
S Sag Sos 
Lower Series. 
Archimedes limestones. 
Shell beds. 
Keokuk cherty limestones. 
Encrinital group of Hannibal. 
Encrinital group of Burlington. 
SSS SS SS 
Argillo-calcareous group of Evans Falls. 
The gritstones (¢) of the upper series are said to be marked 
by the presence of lepidodendron, calamites, and other Car- 
boniferous plants. The sandstones here referred to are, doubt- 
less, the Keosauqua sandstones. Careful search, however, has 
*OweEN, D.D., Geological Survey, Wis., la. and Minn. U.S. Govt., 1852, p. 92. 
