140 
IOWA ACADEMY OF SCIENCE 
Vol. XXIV, 1917 
In the great central plains area of the state there are a num- 
ber of very charming spots, which are all the more noteworthy 
because of their prairie surroundings. Such are the picturesque 
valleys of Willow and Lime creeks at Mason City, where the 
streams have cut the limestone bedrock into steep bluffs and 
precipices which now are margined and covered with forest 
growth. On a still larger scale is the gorge of Iowa river at 
Iowa Falls. Here the river has been displaced within recent 
geologic times and has been forced to cut a new channel through 
Fig. 12. Natural bridge in Jackson county. 
seventy feet of solid limestone. Several small tributaries have 
had to undergo the same treatment and the result is a series of 
gorges and retreats which give the region a rare beauty and 
rugged charm. The older channel of the river is said to be still 
discernible to the south of the present one. 
Steamboat Rock is another locality of geological and general 
interest and there are several others along the Iowa, such as the 
stretch above Iowa City, which owes its rugged character to the 
vagaries of glacial occupation. The older rocky hills were buried 
