210 
IOWA ACADEMY OP SCIENCES. 
that the angle at the point of meeting was very mnch reduced. 
When the angle had thus become small enough, the union of 
currents would practically be perfect from the junction point, 
and thence onward the movement would be nearly directly south- 
ward. The retreat would of course be in the reverse order of 
the advance. This might account for the varying direction of 
strise; for where we find several sets of markings on the same 
surface, the oldest trend more nearly north and south and latest 
more nearly east and west. 
There are other factors entering into this problem. This 
theory supposes that the two ice sheets were contemporaneous, 
and simultaneously moved up to the Mississippi, near which they 
met. Now it is by no means certain that they met at the channel 
of the river. It may have been in Illinois, it may have been in 
Iowa, or it may never have happened at all; for, as already 
intimated, the movements may not have been contemporaneous. 
But whatever doubts there may be concerning that phase of the 
question, it is reasonably sure that the Illinois glacier once 
invaded Iowa. 
The witness most frequently summoned to testify to ice 
movements radiating from the region north of Lake Huron, is 
again called upon. It is the well-known jasper conglomerate. 
Erratics from this Canadian ledge had been found ranging from 
eastern Ohio xo western Illinois. One from Kentucky is figured 
in Wright’s ' ‘ Great Ice Age. ” They are scattered over southern 
Illinois, even as far south as Louisville, in Clay county, where 
Mr. Frank Leverett, of the U. S. Geological Survey, recently 
found one. One has also been found at Alton, 111., twenty-five 
miles above St. Louis, and another at Hamilton, 111., opposite 
Keokuk. So it was pretty definitely settled that this Canadian 
ice stream had invaded the country to the present channel of 
the Mississippi, That it had crossed the river and moved into 
Iowa soil was thought scarcely possible; yet such is now shown to 
have been the case. During the present year two of the jasper 
boulders have been found in southeastern lov/a; one in Des 
Moines county, about six miles from the river, and one near 
Denmark, in Lee county, about twelve miles back from the river. 
The latter was discovered by Mr. Prank Leverett and the other 
was located by myself. Both were fully 200 feet above low 
water in the Mississippi. 
The presence of these Huron erratics at so great an altitude 
and so far back from the river, shows conclusively that the ice 
