986 The American Naturalist. [November, 
in northwestern Iowa. Inoceramus multiplied over the sea bottom as 
oysters, if undisturbed, would crowd a modern oyster bed. Sharks 
disputed possession with the bony fishes and marine saurians. Every- 
thing betokens a deep, clear, open sea that spread away from the shore 
line in Iowa, over all the intervening plain, to the present site of the 
Rocky Mountains. Recent excavations and cuttings have shed much 
light on the Iowa Cretaceous and the present survey which will doubt- 
less add much to our knowledge of this important group of. rocks, 
There are two formations in Iowa, probably belonging to the Cretaceous, 
whose exact stratigraphical relations are at present doubtful, viz.; the 
Fort Dodge gypsum deposits and the Nishuabrtua sandstone. 
The assistant state geologist, C. R. Keyes, contributes several papers 
the most important of which is on the classification of the Iowa forma- 
tions. While in large part merely a summary of the work done upon 
these rocks in recent years by various workers, it also presents someimpor- 
tant considerations derived from the author's personal investigations 
In the revision of the classification, some needed changes in nomen- 
clature appear, as St. Croix for Potsdam, Oneota for Lower Magnesian, 
etc. The attempt to correlate the Iowa rocks with the New York sec- 
tion is wisely abandoned. In the classification of the Lower Carbo- 
niferous, the formations included between the Kinderhook below and 
the St. Louis beds above are grouped together under the term Augusta. 
These beds comprise what Williams’ called the Osage group, a name 
here shown to be inapplieable. 
It is in his discussion of the Coal Measures, however, that the author 
departs most widely from the generally accepted views of Iowa geology. 
After some general considerations of the Coal Measure deposits, he 
calls attention to the two classes of sediments generally recognized, viz. ; 
marginal or shore deposits, and those laid down in the open sea. In 
the Coal measures, as elsewhere, the first of these is characterized by 
rocks predominantly clay, shales and sandstones with practically no 
limestones. The sandstones often form great lenticular masses, some- 
times deeply channelled on the upper surface, the excavations being 
filled with Coal Measure clays. These and many other phenomena 
attest a constantly shifting shore line and the shallow waters. The 
fossils are nearly all brackish water forms or shore species. On the 
other hand, the second class of deposits above mentioned is made up 
largely of calcareous shales with heavy beds of limestone. The for- 
mer are chiefly composed of strictly open sea forms. 
* H. S. Williams, Bul. U. S. Geol. Surv., No. 80, p. 109. 
