190 The American Geologist March, 1892 
with the Mississippi occurs an excessive development of red and 
variegated sandstone. In the vicinity of ‘“Red Rock,” to which 
it has given name, this bed has a maximum thickness of 150 
feet.* The material gathered by the river from this and other 
rocks in its course must have had some part in determining the 
character of the deposit forming about its mouth. 
The Upper Loess.—The upper portion presents the usual char- 
acteristics of typical Loess. A careful examination reveals the 
presence of quartz grains essentially the same as in the ferrugi- 
nous portion, but greatly diminished in number. The main mass 
consists of finely divided particles, rock-flour, varying in size 
from .01 to.05 mm. indiameter. They show no signs of attrition. 
A bare trace of iron oxide may sometimes be observed. No fos- 
sils were seen though the ‘‘lime balls’” or ‘‘loess-kindchen” held 
by some to be derived from fossil shells are common. 
Evanston, Ill. 
EXPLANATION OF PLATE. 
Scale (except in figure 4). fo Amore i 
Fig. 1. Profile section (41g miles) from west to east, through Keokuk 
and Hamilton, I!l., crossing the Mississippi in the vicinity of the lower 
lock of the Des Moines canal. 
Fig. 2. Profile section (314 miles) from southwest to northeast across 
Keokuk Point, starting from a point midway between the mouth of the 
river and Des Moines bridge. : 
Fig. 3. Profile section 34 mile southeast of No. 2, and parallel with it. 
Fig. 4. Profile section on Des Moines from the river to Sixth street. 
1, 2, 3, 4equal 4, 5, 6, 7 of Secrron tr., p. 187. 
ORIGIN OF THE GRAVEL DEPOSITS BENEATH 
MUIR GLACIER, ALASKA. 
By Israet C. Russeti, Washington, D.C. 
| With contributions by Prof. G. FrepERick Wright, Prof. Harry Fielding Reid and Mr. 
H. P. Cushing. | 
In an excellent article on the Muir glacier, in the October num- 
ber of this journal, Mr. H. P. Cushing described the gravels on 
which the lower end of the glacier rests, but states that he is un- 
able to explain their origin. t 
*Geological Report Iowa (1858), Vol. 11, Part 1, p. 168. 
Keyes, C. R., Bull. G. S. A., Vol. nm, pp. 277-292. 
+The same deposits are discussed by G. F. Wright in Ice Age in North 
America, pp. 57-61; and also in AMERICAN GEOLOGIST, Vol. 9, pp. 330-381. 
