IOWA ACADEMY OF SCIENCES. 
211 
sheet must have crossed from the Illinois side and invaded Iowa. 
It may have been that the two streams met somewhere near the 
Mississippi, and the Illinois current being the stronger, crowded 
back its weaker opponent; and then, when the retreat began, 
the Iowa ice field, released from its pressure, may have followed 
up for some time the withdrawal of its adversary. Of course 
the reverse of this might be true. Besides there remains the 
possibility that the culmination on the one side antedated that 
of the other. But in any theorizing the invasion of Iowa by 
the Illinois glacier must be now considered an established fact. 
Whatever may have been the earlier sequence of those move- 
ments, the Iowa ice stream was last to hold possession of the 
western bluff of the Mississippi. For this reason few of these 
Huron boulders will ever be found west of the river. The 
reasons are based on two different kinds of evidence, glacial 
scorings and terminal deposits. In Hes Moines county glacial 
scorings have been discovered at no less than half a dozen 
places.^ In nearly all instances the markings are deep, amount- 
ing to grooves, and, for the most part, remarkably well pre- 
served; so there is no ambiguity as to their evidence. The 
direction varies from 15 degrees east of south to nearly 80 
degrees east of south. This shows either a southeastward or a 
northwestward movement. Now it can be conceived how the 
ice from the Illinois glacier might flow westward, even due 
westward; but the imagination is not elastic enough to account 
for it moving northwestward at the angle indicated by most of 
these scratches. Besides, at least three of the scorings them- 
selves give evidence as to the direction of the ice flow. One 
where the striation of the lateral surface occurs, another where 
the whole face of the bluff is glaciated, and the third where the 
intersecting striae on the level limestone floor tell their story. 
These striae, scratches and grooves give no evidence whatever 
of any other movement than towards the southeast. 
Now as to terminal deposits. It is generally supposed that 
outside of the region occupied by the second ice invasion, mar- 
ginal dejeosits are scarcely to be found. Yet there is no finer 
example of a terminal moraine than maybe seen near Sandusky, 
in Lee county, about six miles north of Keokuk. This ridge is 
about a quarter of a mile from the Mississippi and parallel to it. 
It is about a mile and a quarter long and at its greatest depth 
1 White; Geol. of Iowa, Vol. I, p. 93. 187.0. 
Keyes; Iowa Geol. Sur., Vol. Ill, p. 155. 1893. 
Fultz; Ibid, p. 158. 1893. 
