260 TAe American Geologist. October, 1897 
hill. In the Leaf river valle}'-, the basin valley averages seve- 
ral miles in width, bevels the gently inclined strata of the Hud- 
son River shales, and passes, without deformation, through 
the Galena and Trenton limestones, on to the St. Peter sand- 
stone. The Leaf river flowing eastward and the Elk Horn 
creek flowing southward actually rise in the same basin val- 
ley. The basin valley of Elk Hern creek, 2^ miles southwest 
of Foreston, is several miles in width, and its bottom is under- 
lain, over extensive areas, by the St. Peter sandstone, the Tren- 
ton and Galena limestones having been removed from above 
it. The basin of this stream passes across the Trenton, Gale- 
na, Hudson River, and Niagara formations without the least 
deformation. In eastern Whiteside county, it broadens out 
to form a gently undulating dissected plain, which extends 
from Sterling, 15 miles north, and has a possible width of 10 
miles. It resembles the main Tertiary peneplain, but has an 
altitude 75 feet k)wer, and is bounded on the east, north, and 
west by the higher upland areas which represent the upper 
plain. It bevels the edges of the gently inclined strata of the 
Galena and Niagara limestones, and the Hudson River shales. 
It is literally a peneplain. 
At Unionville, in Whiteside county, Ave ascend out of the 
canon valley of Rock creek, on to a dissected plain which bor- 
ders the valley and averages 75 feet above it. A few miles 
northwest we have climbed a long slope on to an upland 
ridge which, upon tracing it northward, we find to be a rem- 
nant of the main Tertiary peneplain. It is here about 75 feet 
above the lower peneplain. We now travel northward on the 
"Mississippi divide," which is a broad flat-topped even-crest- 
ed upland ridge trending north and south a few miles east of 
the Mississippi river. On our right is the broad shallow basin 
valley of Rock creek, trenched by its canon valleys, and bound- 
ed on the opposite side by an even-topped upland area corre- 
sponding to that on which we stand. On our left every small 
stream, tributary to the great river, has its basin valley from 
one to two miles in width, separated from each other by even 
crested ridges which extend out as great spurs from the main 
divide. Some of these basin valleys are trenched into Niag- 
ara limestone, some into Hudson River shales, and still others 
into Galena limestone, but there is no difference between 
them except in width and in the state of their preservation. 
