286 The American Geologist. ^^y- ^^os. 
tances. Still, granting that they have been there and have been 
removed, their removal must have been effected by a river whose 
water surface was lower than the Wisconsin terrace. The bight 
of a Wisconsin terrace according to professor F. A. Wilder's''' 
careful discriminations, in Lyon county, on the Big Sioux 
river, which is about 300 miles farther up the Missouri val- 
ley, is ten feet above the adjacent fioodplain, continuing to the 
mouth of the Big Sioux. According to Mr. Upham this ter- 
race is still visible between the mouth of the Big Sioux and 
Council Bluffs, the most southern point still being 140 miles 
from Concannon's farm. This terrace, so far as known has 
not been identified at lower points, and it doubtless disappears 
in the present floodplain of the Missouri river at many miles 
north of the Concannon farm. 
Corroborative of this conclusion is the interesting presen- 
tation of the descent of the Wisconsin terraces by professor 
J. E. Todd. According to his tabulation the descent of the 
lower "bouldery terraces" (the Wisconsin terrace?) along 
the Missouri is as follows (Bulletin No. 158, U. S. Geol. Sur., 
p. 137), measured by aneroid: 
Opposite Niobrara its hight is 200 feet. 
Niobrara, S. Dak 210 " 
Yankton, S. Dak 140 " 
Vermilion, S. Dak 100 
Blair, Nebraska no " 
Calhoun, Nebraska 100 
Bellevue, Neb. (8 ms. S. E. of Omaha) . . 70 
Measured as the crow flies the distance from Niobrara to 
Bellevue is about 150 miles and the descent is about .93 foot 
per mile faster than the descent of the river. The distance 
from Bellevue to Lansing, measured in the same way, is about 
150 miles. If the same relative rate of descent were continued 
below Bellevue the descent of the Wisconsin terrace to Lans- 
mg would carry it 69.5 feet, below the surface of the river, at 
Lansing. Owing, however, to the roughness of this calcula- 
tion, and to the uncertainty of the data on which it is based 
(aneroid levels), its chief value consists in showing the south- 
ward lowering of the Wisconsin terraces, and the certainty 
of their being lost in the present floodplain at an indefinite 
* Iowa Geological Survey, vol. x, 1900. 
