IOWA ACADEMY OF SCIENCE 
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of the stream is very sinuous, curving riverward around the salients 
and forming re-entrant angles landward at the mouth of every 
tributary valley or ravine. Furthermore, the opposite sides of the 
valley show little tendency to anything approaching exact parallel- 
ism. Between Lansing and Dubuque, — a portion of the river ar- 
bitrarily chosen to illustrate certain features equally well developed 
elsewhere in the upper valley, — the lateral stream courses show 
all the characteristics of the normal type of topography, mature or 
approaching maturity. The sides of the valleys are broadly di- 
vergent; the salients are normally rounded, with front slopes and 
side slopes approximately equal; and there is no very strong sug- 
gestion of parallelism between the opposite sides. The Turkey 
river or the Little Maquoketa may be taken as illustrations. While 
there are some steep cliffs along these streams, they are not con- 
tinuous, and those occurring on one side usually face lateral valleys 
or rounded slopes on the other. The main valley, on the other hand, 
has the salients truncated, the projecting spurs cut away as if sliced 
off vertically. The ridges between the side valleys end in frown- 
ing precipices while the side slopes retain the characteristics of 
mature topography (Fig. 1). All short curves have been straight- 
ened out as if some great gouge had been driven down the channel, 
reducing it to a uniform width, clipping off the rounded points and 
making the walls precipitous, so that vertical bluffs in Iowa face 
parallel vertical bluffs in Wisconsin (See map, Fig. 2). The preci- 
pices are not due to recent undercutting caused by the swinging of 
the current from one side of the channel to the other. Their par- 
allelism and continuity can not be so explained, and then they pre- 
sent precisely the same characteristics whether the river flows 
directly at their feet or is separated from them by one or two miles 
of sloughs and islands (Fig. 3). Neither can the precipices be 
attributed to the kind of rocks in which the river gorge has been 
cut, for the walls show rocks of many ages and are of many degrees 
of hardness, varying from hard limestones to very friable sand- 
stones and soft shales. Furthermore, the tributary streams have 
cut through precisely the same kinds of rocks, and yet their val- 
leys, at least on the Iowa side, show normal characteristics. 
By way of explanation of the peculiar features noted in the 
major stream there may be offered the probability that the gravel- 
laden Wisconsin floods were the gouge which cut away the bases 
of the well-rounded projecting spurs and developed the succession 
of parallel rock cliffs on opposite sides of the river. As shown in 
figure 1 the side slopes and back slopes of the spurs still retain all 
