Review of Recent Geological Literature. 183 
Assistant State Geologist. Pages 572; with 8 geological maps of coun- 
ties, 13 plates, and 56 figures in the text. Ues Moines, 1899. 
One third of Iowa has been mapped in detail, including thirty-three 
counties, seven of which were surveyed during the year 1898. Besides 
the administrative report of Prof. Calvin, the present volume contains 
reports on five counties, namely, Carroll, by H. F. Bain; Humboldt, 
by Prof. T. H. Macbride; Story, by Dr. S. W. Beyer; Muscatine, by 
Prof. J. A. Udden; and Scott, by Prof. W. H. Norton. For Carroll 
and Humboldt counties, a single map of each is presented, showing 
the d'.ift formations and the very restricted exposures of the underly- 
ing rocks; but each of the other three counties has two maps, one 
noting the surface deposits, and the other the older rock formations. 
There is also a paper on Mineral Production of Iowa in iBgS, by Dr. 
Beyer; and a Report of the Artesian Wells of the Belle Plaine Area, 
by H. R. Mosnat. 
The value of the chief mineral products is stated as follows; Coal, 
$5,123,187; clay, $2,057,022; stone, $563,586; and lead and zinc, $43,784; 
in total, $7,787,579. To this ought probably to be added about $75,000 
as the value of the gypsum product, for which exact figures were not 
obtained. 
Each of the county reports well describes the topography and the 
geology, stratigraphic, glacial, and economic. It is evident that ex- 
cellent progress is being made in thorough investigation of the geo- 
logic history and resources of Iowa. With the careful exploration and 
study already given to so many counties, distributed in all parts of the 
state, the work of the survey may be regarded, probably, as half done, 
since its general outlines and principles have now been mainly de- 
termined. 
The classification, areal and time relations, and conditions of origin 
of the complex series of drift formations, already quite satisfactorily 
ascertained, are perhaps together the most important contribution of 
the Iowa survey to the advance of American geology; in which, how- 
ever, this state owes much to earlier and to contemporaneous workers 
in the adjoining states. While we may still, according to the opinion 
of the reviewer, consider the Glacial period as continuous for the con- 
tinent, it was divided in Iowa, near the boundary of the continental 
ice-sheet, by intervals of great recession and readvance of the ice- 
fields. 
In this upper part of the Mississippi river basin the Ice age was 
more complicated, apparently, than in either the Atlantic or the Pacific 
coastal region, or in the interior of Canada. Five distinct and suc- 
cessive deposits of till are recognized in the parts of Iowa here re- 
ported, alternating with interglacial beds, zones of weathering, and soil 
formation. The series represents, as may be thought, stages of the 
oncoming, culmination, and wane of a single continental Ice age; but 
if we regard this state alone, it records at least two epochs of snow 
and ice accumulation, divided by a long epoch of deglaciation. 
The pre-Kansan till, perhaps to be correlated with the Albertan 
