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IOWA ACADEMY OF SCIENCE 
Vol. XXIV, 1917 
pure sand, form cliffs and grottoes and nooks of marvelous colors 
and patterns, set off by groves and lanes of shady trees. 
At Guttenberg and again at the mouth of Turkey river are 
high narrow ridges nearly a mile in length which separate the 
tributary valleys from the valley of the Mississippi. The Gut- 
tenberg ridge is over 200 feet high, with a gentle slope to the 
south, and the Turkey river ridge is nearly as high and termi- 
Fig. 11. Castle Rock at mouth of Turkey river, Clayton county. 
nates in a bold rock tower which stands almost a hundred feet 
above the rivers on either side. These ridges of course owe their 
existence to the hard, resisting beds of rock which underlie the 
country and which withstand to the last the encroachments of 
time and the destroying elements/ 
And so one might continue this enumeration at great length, 
but it must be concluded with one or two more examples before 
