250 The American Geologist. October, i«97 
esenrpruent to the verge of the Mississippi canon valley, and 
the same across the Lower Magnesian plain northward to the 
north line of the county. The canon valleys are trenched from 
400 to 450 feet beneath the surface of the plain, except along 
and near tlie Mississippi river where their depth is nearly 600 
feet. In Houston county, which is the most southeastern in 
the state, and lies southeast of Winona county, the Lower 
Magnesian plain is represented by most of the upland ridges, 
which stand about ]L50 feet above the sea, rising to 1200 feet 
in portions of the county. These upland ridges form a near- 
ly level dissected plain which terminates abruptly near the 
verge of the Mississippi canon valley. It is cut by the deep 
valleys of streams tributary to the large river, but proportion- 
ately slightly wider than the great caiion. The water level is 
about G20 to 700 feet above the sea, the main valleys being 
thus about 500 feet in depth. The Lower Magnesian plain 
slopes gently westward, with the dip of the strata, ten miles 
to the foot of the Trenton escarpment, where the surface rises 
abruptly 100 feet to the top of the Trenton limestone, and 
then by a more gentle slope of 50 to 75 feet, reaching the lev- 
el of the Trenton plain about 1325 feet above the sea, or about 
150 feet above the lower plain. 
In going westward from Houston county, we again get into 
very interesting territory. In Fillmore county, the general 
upland surface averages 1200 feet above the sea, except on 
the Trenton limestone areas, where it rises abruptly to 1300 
or 1350 feet. Trenton outliers stand on thelower plain some- 
what as do the "mounds" in the lead region of Wisconsin, 
Iowa, and Illinois. They are known as "Trenton mounds." 
In the western portion of the county, the nearly level i)lain 
which forms the surface of the Trenton areas, passes across 
the intervening strata on to the Devonian limestone, without 
any deformation. Perhaps I should say that while both the 
Devonian and Trenton plains may be "structural" in origin, 
their surface corresponds in altitude, forming a practically 
continuous dissected plain, having a general altitude of 1300 
to 1350 feet above the sea, suggesting that they may have 
been formed under the same conditions as a true peneplain. 
This apparent peneplain is not confined to one county, but 
passes westward across Mower county, gently declining in 
