Quaternary Geology.— Gordon. 183 
Owing to their proximity to the Chesapeake formation, and the 
broken and water-worn condition of the shells it is possible, if not 
probable, that they were derived from the underlying formation, 
The soft, loose Chesapeake sands at this locality were never richly 
fossiliferous and have lost their shells by solution, but there are 
other localities, not far from Heathsville, where both Venus mer- 
cenaria, Gnathodon and other Miocene shells occur in abundance 
in the Chesapeake formation. 
QUATERNARY GEOLOGY OF KEOKUK, IOWA, 
WITH NOTES ON THE UNDERLYING ROCK 
STRUCTURE. 
By C. H. Gorpon, Evanston, Il. 
While the Keokuk limestone with its very interesting piscine 
and crinoidal fauna, and the shales with their peculiar siliceous 
deposits, have made this locality widely noted, the special topo- 
graphical and stratigraphical features of the region have received 
comparatively little attention. We have noted already some of 
the important features pertaining to the lithified deposits*, and it 
is the purpose of this paper to consider the equally significant 
topographical and Quaternary features. 
Keokuk is situated in Lee county, which comprises the triangu- 
lar area at the junction of the Mississippi and Des Moines rivers, 
in a bend of the Mississippi about two miles above its confluence 
with the Des Moines. Fora distance of eight miles above the 
city, the general course of the river is due south with a slight 
bend to the west. Opposite Main street it makes a sharp turn to 
the west, bearing off s. w. by w. for nearly three miles, where it 
is joined by the Des Moines and again resumes its southerly course. 
From Montrose, nine miles above, the river flows over the cherty 
layers at the junction of the Burlington and Keokuk beds, giving 
rise to what is known asthe Des Moines rapids. The canal along 
the western bank, constructed and maintained by the government 
to overcome this impediment to navigation, constitutes one of the 
important engineering features of the river. Just below the 
lower lock, an iron bridge spans the river, connecting the city 
with Hamilton, a thriving village on the Illinois side; while a few 
*AMERICAN GEOLOGIST, Oct., 1889, p. 237; same, May, 1890, p. 257; 
American Naturalist, April, 1890, p. 305; American Journal of Science, 
Oct., 1890, p. 295. 
