322 The American Geologist. May, 1895 
pal exposures are found on Crooked creek, Davis creek, and 
on English river. In Keokuk county the best exposures oc- 
cur on the Skunk river where the rock is brought above the 
water level by a series of small anticlines. 
KiNDEllHOOK. 
The rocks which may be considered as belonging to this 
formation, as at present defined, are exposed principally in 
Des Moines, Louisa and Washington counties. It is the ex- 
posures in the latter county which have been particularly 
studied. The outcrops occur along Davis and Goose creeks 
and up English river to a mile or more beyond Wassonville. 
Three well marked divisions are found: the Wassonville lime- 
stone, English River gritstones and Maple Mill shales. 
Wassoncille limestone. — This is an earthy magnesian lime- 
stone, in places becoming arenaceous. It is fossiliferous and 
is traversed by chert bands, which are also full of fossils. 
As exposed at the old Wassonville mill and in that neighbor- 
hood, it attains a thickness of about thirty-five feet. It is not 
always sharply separated from the bed below. 
Unglish liicer (jritstones. — At a number of points from Ka- 
lona to Wassonville this bed is seen just below the Wasson- 
ville limestone. It is a fine-grained, buff to white sandstone, 
or gritstone, to use Worthen's name, and is exceedingly fossil- 
iferous, the forms being preserved as casts. The fauna pre- 
sents a general agreement with the "yellow^ sarid layer" at 
Burlington. The relations between the gritstone and the 
limestone are intimate. 
The gritstone is usually sharply divided from the underly- 
ing shale, as at Maple Mill, where a two-inch band of non- 
fossiliferous limestone separates them. Near Kalona, however, 
they are interbedded. It has a maximum thickness of about 
twenty feet near Maple Mill, but farther east feathers out 
and disappears. At the Riverside mill the limestone rests 
directly upon the shale. 
Maple Mill sltale. — The lowest member of the central Iowa 
Kinderhook is a non-fossiliferous, dark green to blue argilla- 
ceous shale, which is exposed at a number of points on English 
river. It has a maximum exposure of less than thirty feet, 
but is known to be considerably thicker. Probably 200 feet 
is nearer the correct thickness. The Kinderhook of south- 
