374 J^J^^ Afiicrican Geologist. Docomber, i899 
around the foot of the Niagara escarpment the surface of the 
Maquoketa area presents a series of long, rain-sculptured, cul- 
tivated slopes, rather steep, but gradually blending into the 
more level area encountered after passing from the rugged top- 
ography of the Galena limestone to the more softened forms of 
the Maquoketa, near Julien. 
A mile or two east of Peosta, the deep trenches and steep 
scarps charactertistic of the margin of the Niagara limestone 
are encountered. Erosion has here produced picturesque ef- 
fects, not so pronounced maybe, but yet in a measure compar- 
able with those seen in the region occupied by the Galena lime- 
stone. The base of the Niagara is somewhat softer than the 
Cialena. Not far above the base are rapidly weathering beds 
containing a large amount of chert. As a result of differences 
in structure there are fewer vertical precipices in the Niagara 
than in the Galena area, and this is particularly true when the 
clififs are formed by erosion of trenches in the basal portions of 
the Niagara formation. Talus material accumulates at the 
foot of the scarps, and the upper part of the clifT faces recedes 
as an effect of weathering. While the resulting slopes, as a 
rule, are not vertical, they yet stand at high angles; and so the 
transition from the area of Maquoketa shales to that of the Nia- 
gara, is marked by an abrupt and steep ascent of sixty to a 
hundred feet. This sharply defined offset is one of the most 
striking topographic features in this part of the driftless area. 
On the line follow^ed by the Illinois Central railroad the 
edge of the Niagara does not extend far beyond the margin of 
the Kansan drift; but south of the valley of Catfish creek, and 
conspicuous even from the car window, the Niagara gives 
character to a high ridge, noted above, which extends two or 
three miles into the driftless area; and at Sherrill's Mound, in 
the northern part of the county, the Niagara escarpment is 
nearly ten miles east of the edge of the drift. The drift-covered 
area is entered by the railway line less than a mile east of 
Peosta. A cut, thirty to forty feet in depth.- is made in the 
thickened margin of the Kansan till one-half mile east of the 
village named; and at the station the traveler has at last an un- 
interrupted view to the western horizon. He has reached the 
upland plain, a plain which varies but little in altitude all the 
rest of the way across the state. He has passed from the drift- 
