108  W. Upham—Minnesota Valley in the Ice Age. 
county between Carver River and Beven’s Creek. On this — 
tract, composed, below the soil, of stratified gravel and sand, 
extending about two miles in width and elevated 125 feet above 
the river, are frequent depressions from ten to thirty rods in 
diameter and fifteen to forty feet in depth below the general 
level, often enclosed without outlet, and some of them contain- 
ing lakelets and sloughs. Such hollows have not been seen 
_ elsewhere in our exploration of these terraces along the Minne- 
sota Valley, which instead have generally a smoothly level 
contour. Their origin must apparently be referred to sedimen- 
tation while masses of ice occupied the places of these bowl- 
like depressions. Elsewhere the absence of such inequalities 
_ In the surface of the valley drift, as also the very rare occurrence 
of bowlders in it, and the fact that no portion of it, excepting 
that just mentioned at Chaska, is known to be interglacial by 
having become covered with till, together show that the depo- 
sition of these beds of modified drift took place outside the 
limits of the retreating ice-sheet. The valley appears to have 
remained from excavation in an interglacial epoch, and to have 
become rapidly filled with sediments as soon as the ice by 
which it had been enveloped was melted away. 
Alluvial beds fill the Minnesota valley at Belle Plaine, as 
shown by the section of the salt-well, to a depth about 150 
feet below the present river at its stage of low water. This 
_ well, situated on the bottomland at nearly the same height 
with the depot, or approximately 30 feet above the river an 
725 feet above the sea, is reported bv Professor Alexander 
_ Winchell to have passed through the following succession 
- deposits before reaching the bed-rock : soil and gravel, 9 feet ; 
clay and gravel, 9 feet; sand and gravel, 18 feet; quicksand, 
54 feet, having its base 90 feet below the surface ; coarse sand, 
1 foot ; clay, 6 feet, in which was found, two feet from its top, 
a piece of grapevine with bark; sand, 38 feet, varving from 
quicksand to coarse sand, in which at 114 feet, inflowing water, 
under pressure from the bottom, filled the pipe twelve feet 
with sand, and a second time, at 125 feet, filled it five feet > 
then gravel, quicksand, and coarse sand, 45 feet, having its — 
base 180 feet below the surface, yielding water at 144 feet, 
which filled the pipe with sand ten feet, and containing another — 
piece of grapevine at 168 feet; next, from 180 to 200 feet, blue — 
clay, 7 feet, and rock fragments, 13 feet, probably both bowl- — 
-der-clay or till; and, lastly, gravel, 2 feet; the whole depth of 
alluvium and drift being thus 202 feet, extending about 170 
feet below the river. : 
At the railroad bridge which crosses the Minnesota rivet — 
lose to its mouth, borings were made to a depth of 60 feet 
below the river-bed without reaching the bed-rock. In the — 
