Editorial Comment. 271 
for the first time clearly deciphered, includes the following 
succession of events, each of which has had its influence in 
determining the present condition aiid characteristics of Iowa 
soils. 
I. First stage of glaciation, Albertan. Invasion of Iowa 
by glaciers and distribution of lowest sheet of till. 
II. First interglacial stage, Aftonian. Melting and retreat 
of glaciers and deposition of gravels, followed by a long 
period of forest growth, development of soils, and modification 
of the original drift. 
III. Second glacial stage, Kansaii. Cold more intense and 
glaciation more general than during the first stage. Distri- 
bution of McGee's lower till. 
IV. Second interglacial stage, Buc/iriuan. Introduced by 
deposition of gravels in Buchanan, Klack Hawk, Floyd, Cerro 
Gordo and other counties. This stage was very long and the 
surface of the second drift sheet was profoundly modified by 
erosion, oxidation and leaching before it came to a close. 
V. Third stage of glaciation, Illinois. During this stage 
only a small part of Iowa, embracing portions of Louise, Des 
Moines and Lee counties, was invaded by glaciers. The ice 
came from the northeast, bringing boulders from the eastern 
shores of lake Huron. 
VI. Third interglacial stage (unnamed), during which the 
modification of the second drift sheet proceeded over the 
greater portion of Iowa. The small area occupied by the third 
deposit of drift also suffered more or less of modification. 
VII. Fourth glacial stage, louuui. During this stage the 
northern half of Iowa was overrun by glaciers The southern 
limit of this incursion may be traced a few miles north of 
a line drawn from Iowa City to Des Moines, and then deflected 
northwestwardly to Plymoutii county. It was during this 
stage that the enormous granite boulders so conspicuous in 
Hremer. Black Hawk. Buchanan and other counties in north- 
eastern Iowa were transported and deposited where they now 
lie. 
VIII. F'ourth interglacial stage Toronto (?). This fourth 
interglacial stage was short as compared with the second, and 
probably with the third. The amount of erosion, oxidation 
and leaching that during this interval took place in the sur- 
