16 
IOWA ACADEMY OF SCIENCE 
of the United States Geological Survey. Near Yarmouth in Des Moines county, 
soil and peat belonging to this horizon are well developed, and these have 
furnished remains of at least two types belonging to the recent fauna, the 
wood rabbit and the skunk. Between the Aftonian and the Yarmouth changes 
in the life of the continent had taken place, hut our knowledge of the Yarmouth 
deposits and the fossil mammals they contain is as yet too meager to enable us 
to say how great the changes were. 
Extensive beds of gravel, ' probably representing the beginning of the Yar- 
mouth interval, were deposited by floods at the time the Kansan ice was melt- 
ing. These have been called the Buchanan gravels. They attain their best 
development in the northeastern counties of the. state, but they are known as 
far south as Iowa City, and they have furnished enormous quantities of rail- 
way ballast near Leroy in Minnesota. For railway ballast, for the improvement 
of village streets and country roads, for all grades and phases of cement con- 
struction, for ordinary building sands, the Buchanan gravels so generally dis- 
tributed in Delaware, Buchanan and other northeastern counties as to be con- 
veniently available in almost every neighborhood, furnish ideal materials prac- 
tically inexhaustible. For reasons easily understood and fully set out in some 
of the reports the Buchanan gravels occur on the uplands as well as in what 
were sags and valleys in the ice moulded surface of the Kansan drift, and it is 
to this fact that we owe their presence in almost every neighborhood, no matter 
where located. 
There are some beds of rather fine, stratified sand distributed along the 
stream valleys which originate in the Iowan plain, referable to the relatively 
meager floods which resulted from the melting of the Iowan ice. The deposits 
are unimportant commercially, but they help to illuminate and unify the com- 
plex history of the Pleistocene period, and every phase of this history is of the 
utmost importance to the inhabitants of Iowa. 
As the work of the Survey has conclusively demonstrated, the gravels depos- 
ited in connection with the melting of the Wisconsin ice, at the very dawn of 
postglacial time, are by far the most extensive of all the Pleistocene deposits 
of similar character and origin. In the north-central counties of the state great 
sheets of gravel cover areas equal to entire townships, while gravel kames and 
eskers are distributed as conspicuous knobs and ridges over much of the sur- 
face embraced in the Wisconsin area. These gravel ridges culminate in Ochey- 
edan Mound in Osceola county, a great kame rising 100 feet above the surround- 
ing prairie, keeping watch over a radius of twenty-five miles or more, its summit 
well worthy of the distinction which it reputedly holds of being the highest 
point of land in Iowa. For detailed studies of the Wisconsin drift, of the 
associated sheets and ridges of gravel, and of the characteristics and geographic 
position of the Altamont moraine on the western side of the Wisconsin lobe, 
the Survey is indebted to the painstaking work of Professor Macbride. 
Iowa is rich in its possessions of another Pleistocene deposit of incalculable 
economic importance, the Loess. No subject has been more misunderstood, no 
subject has given rise to more uselss and meaningless controversy, no subject 
has been responsible for more grotesque and untenable hypotheses as to its 
origin and original distribution, than the Loess. Iowa offers unsurpassed op- 
portunities for the study of this remarkable geological deposit, and an Iowan 
who has given some time in recent years to Survey work, but who had critically 
^studied thousands of loess sections years before the Survey was organized, has 
