IOWA ACADEMY OP SCIENCE 
69 
graph made possible by the wealth and variety of material afforded largely by 
the Devonian limestone near North Liberty, Johnson County, Iowa, though 
other localities contribute some excellent material. 
Volumes not specifically mentioned above are given to county reports almost 
wholly. While space will not admit of referring in detail to the contents of 
each of these reports, it is proper to characterize them collectively as being 
rich in data respecting the various geological features to be observed in the 
counties under consideration whether of merely local or of general interest, 
and which can be made use of in the preparation of volumes on the stratigraphy, 
•physiography, palaeontology, and other subjects involving the state as a unit. 
Whenever a county contains some particular phase of geology presented in an 
unusually favorable manner or degree, such a county has been assigned to 
someone particularly well qualified along that line, even though that feature 
may already have been handled in a monographr in some previous volume. 
Thus the subject gets a later consideration and at the hands of a second investi- 
gator. A few instances in illustration may be given. Leonard’s monograph on 
lead and zinc in Volume VI. is well supplemented in the Dubuque County 
report in Vol. X., by Calvin and Bain. Wilder’s report on Webster County 
contains a very valuable monograph on Gypsum and the Gypsum Industry, while 
the loess has received much, attention in various reports. Shimek in his report 
on Harrison and Monona counties finds opportunity to give the public the 
benefits of his latest studies upon that most interesting formation. Similar 
remarks apply to his treatment of the Aftonian Stage in the same report. The 
temptation is strong to multiply instances. In fact, every subject of the geologi- 
cal interest in the state has been given special consideration time and again. 
I can not forbear to mention the Pleistocene series in a paragraph by itself, 
however. 
Calvin in Volume XII., of the Survey says, “The work of our geologists, in 
co-operation with members of the U. S. Geological Survey, has made Iowa 
classic ground for the study of problems relating to the drift. The succession 
of events which took place during that most interesting and most unique of 
all the divisions of geological time, the Glacial Epoch, is more clearly recorded 
in Iowa than anywhere else on this continent.” The history of geology in Iowa 
in the past twenty-five years shows a remarkable advance in the solution of 
the problem of the drift. Keyes, in his article on the Geological Formation of 
Iowa in the first volume of the Survey published twenty years ago, says the 
drift is made up in Iowa of two sheets, the upper and the lower till. Now, if 
we concede a place in the list to. the Iowan, a condition I make only because 
of the doubt thrown upon it by Leverett within the past few years, there are 
five glacial and four interglacial stages definitely displayed and established 
within the bounds of the state. Involved with these are the loesses, gumbo, or 
the Loveland, as Shimek is pleased to term it, the Buchanan gravels and several 
other more or less differentiated deposits; nearly all of which have been placed 
beyond doubt as to identity, relations, etc. An annual report of the mineral 
production of Iowa was begun in Volume VIII. This has been in charge of 
Prof. Beyer in all the succeeding volumes and has proven a valuable feature 
of the reports. The annual administrative reports of the State Geologist often 
contain noteworthy discussions of subjects that have an important practical 
