144 Sioux City Academy of Science and Letters. 
Valleys of minor streams.—Into the embayment at 
Jackson and out along the foot of the escarpment to the 
southeast flows Elk Creek, previously mentioned, and at 
other points, notably near Hubbard and Homer, the 
escarpment gives away to gently sloping valleys through 
which Pigeon and Omaha creeks emerge on the flood 
plain and unite with Elk Creek. The valley of Elk Creek 
is comparatively broad, and base leveled below the vil- 
lage of Goodwin, with a well-developed flood plain 
through which the creek meanders. That this valley 
suffered a deep erosion similar to that of the Missouri is 
indicated by a drill hole on the north bank of the creek 
on the farm of Mr. Ryan in sec. 27, about 2 miles above 
Jackson. (See fig. 4.) No consolidated material was en- 
countered within 100 feet, and between 75 and 90 feet 
Stream gravel or interloessal till was passed through, 
while drillings made on one side or the other of the val- 
ley just within the edge of the flood plain indicate the 
normal occurrence of the strata at depths of 30 to 40 feet. 
Terraces.—The modern flood plains of the Missouri 
and Elk Creek are strictly recent terraces of those 
streams. Todd* has differentiated in the region farther 
up Missouri and Big Sioux rivers a higher bowldery ter- 
race (earliest), a lower bowldery terrace (later), and a few 
silt terraces of still later date. On the Iowa side of Mis- 
souri River southward from Sioux City may be recognized 
remnants of several terraces, but on the Nebraska side 
through Dixon and Dakota counties there are no good 
traces of terraces along the escarpment. Erosional dis- 
section has proceeded farther on the west than on the 
east side of the valley but not to such anextent as to 
have obliterated all evidences of former terraces. 
Ox-bow lakes.—Much of the land adjacent to Missouri 
River is considered of very uncertain life owing to the 
tendency of the stream rapidly to erode its banks wher- 
ever the current is deflected against them, and to erode, 
overflow, and cut the narrow necks between the curves of 
a loop. Many square miles of land have been lost in this 
way, and much more has gone from the jurisdiction of 
one State to that of another by the erratic course of the 
river. Land is of course formed to a certain extent by 
aTodd, J. E., The Moraines of southeastern South Dakota and their 
attendant deposits; Bull. U. S. Geol. Survey, No. 158, 1899, pp. 128-140. 
