The Loess and the Lansing Man. — Shimek. 361 
part of the ice-mass persisted year after year the climate must 
have been such that snails of the species which we find in the 
loess, and the plants which they required for food, could not 
have existed. Glaciers in mountainous regions are not to be 
compared with such a mass, and do not necessarily indicate a 
cold climate. A difference of a few feet in altitude, or the 
protection offered by a sheltered valley or ravine, may be suffi- 
cient to preserve a small glacier even in a climate in which 
plants may grow abundantly. The writer has seen a profuse 
mass of summer flowering plants growing against the side of 
an ice-house within two feet of a great mass of ice ! But im- 
agine plants and snails growing in such a region as is pictured 
by McGee in pi. LX, p. 575 of his great report! 
The third assumption is untenable. It would be remarkable 
indeed if over the greater part of the loess-covered region the 
assumed loess-silt originally filling the valleys should have 
been removed with such nice exactness that a practically uni- 
form thickness remains covering the irregularities of the drift 
surface beneath, on sides and tops of slopes, even on opposite 
sides of the same ridge, and hence in different drainage areas! 
Moreover, loess frequently shows a lamination parallel with 
the present surface, and hence not often horizontal. This is 
especially noticeable in northeastern Iowa, where the loess-sheet 
thins out, as for example in most of the exposures north of 
Decorah. 
The fourth assumption, that loess is of the Iowan age, has 
a certain amount of foundation in fact, but is unwarranted in 
the extent of its attempted application. It is based on the in- 
vestigations and reports of the geologists of the Iowa Geolog- 
ical Survey,* who investigated the loess in some of the counties 
along the border of the Iowan drift. All the Iowa references 
cited have special reference to this restricted area, and in most 
cases the authors specifically so state. Bain (1. c. p. 461) says : 
"The loess found in the region has been referred to the Iowan 
since it is believed to be in this region the equivalent of the 
Iowan drift farther north, and now in part buried under the 
♦Calvin, s.. in. Oeol. 8ur., vol. vii, p 89. i s 'i7 : vol. viii, pp. it:: t. 216, 
]8!>S; Bull. Geol. Boo. 0/ \ ,„ . . vol. x. p. 11n. 1890. Bain. IT. Fostbb, hi . 
Oeol. Bw., vol. v. pp. 155-6, 1896; vol. \i. pp. 161-3. 1897. Bbybb, s 
W., la. Oeol. Bur., vol. vii. p. 236, 1897; vol. x. p. 281, 1900. I.i:vi:heti, 
Fhank. of the T*. s. Geol. Survey, also tentatively refers a pari •<( tli" 
loess of Illinois to the iowan. Sec / . .*. Oeol. Bur., vol. xxxvili, p. 153, 
1899. 
