1887] . Mineralogy and Petrography. 761 
through Pocahontas and Webster Counties to the northwest 
corner of Boone County; thence eastward to the north-central 
portion of Story County; thence north into southwest Franklin 
County, and from that point to the northwest through Wright 
and Hancock Counties to Forest City, in the southeast part of 
Winnebago County; thence to the northwest to the northeast 
corner of Kossuth County; thence curving to the southeast, 
“forming an interlobular portion to the east side of Winnebago 
County ;"* thence uniting with the ‘outer moraine, as it cuts 
_ across the northwest portion of Worth County, and enters Free- 
_ born County, Minnesota. 
k “These moraines are linear bends of knobby drift, and struc- 
= turally are developments of the till, having similar features with 
_ it, except that their altitudes are exaggerated.”* They were 
_ formed by an extension or “ finger” of the main mass of ice at 
the north; the one which formed the outer moraine reached a 
point some distance south of Des Moines, but there stopped in 
its course by the action of the warm south winds and the sun, 
which soon caused it to retreat to the north, beyond the limits: 
of the State; but only to again advance at a colder period, but 
3 time with diminished volume, and to be soon driven back 
_ gain by the winds and the sun. ; 
4 dia second advance of the ice-sheet the inner moraine was 
An extended study of the drift and loess formations of the 
entire State would doubtless throw much additional light upon 
“ie evidence of the ice-flows and the condition of things within 
! borders of the State during and at the close of the glacial 
— *poch.— Clement L, Webster, State University, Towa. 
MINERALOGY AND PETROGRAPHY- 
Hip J. E. Todd, Iowa Hort. Rept., vol. xviii. 
5 Edited by Dr. W. S. BAYLEY, Madison, Wisconsin. | 
Seether Naturalist, Dec. 1885, p. 1216. 
logical Magazi 886, 
2 
agazine, vii., Dec. 1886, p. 81. 
ia 
