Sioux City Academy of Science and Letters. 145 
these shiftings of channel but not enough to compensate 
for that removed, and such made land, as for instance, 
that formed by the silting up of the ends of ox-bow lakes, 
is slow in attaining a state in which it becomes of value 
to man. 
Recent examples of such processes are McCook and » 
Goodenough lakes in Union county, which were formerly 
a part of the river channel, the land lying within the 
loops having been then in the State of Nebraska. The 
latter neck was cut through in the spring of 1900, after 
having been first ditched by the farmers of the locality. 
GEOLOGY. 
Historical statement.—The study of the general geol- 
ogy of the middle and upper Missouri Valley dates from 
the expedition of Lewis and Clark in 1804-5. These ex- 
plorers noted the exposures of sandstone in the Black- 
bird Hills and at Ponca, Nebraska. As early as 1820 
fossils were collected from this region that a dozen years 
later aroused a lively interest in the age of the rocks. 
Henceforth for many years the visits of American and 
European geologists to this locality were frequent, and 
resulted in an extended discussion relating especially to 
the age of the basal sandstone of the region. It was not 
until 1856 that Meek and Hayden constructed a definite 
section of the rocks. In 1861 this section which was so 
long a standard of comparison was further revised and 
names were given to its five members. 
Among the official reports that deal with the geology 
of the region are: First Annual Report of the United 
States Geological Survey of the Territories, embracing 
Nebraska, by I. V. Hayden, 1867; Geology of Iowa, Vol. 
2, 1870, by C. A. White; lowa Geological Survey Reports, 
Vol. 1, 1892, and Vol. 3, 18938, by S. Calvin; and Vol. 5, 
1895, by H. F. Bain; The Moraines of southeastern South 
Dakota and their attendant deposits, by J. E. Todd, 
Bull. U. S. Geol. Survey No. 158, 1899; The Colorado for- 
mation and its invertebrate fauna, by T. W. Stanton, 
Bull. U.S. Geol. Survey No. 106, 1893; Preliminary report 
on the geology and underground water resources of Ne- 
braska west of the One Hundred and Third Meridian, by 
N. H. Darton, Prof. Paper U. S. Geol. Survey No. 17, 
1903. 
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