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IOWA ACADEMY OF SCIENCE Voi. XXIV, 1917 
the bluffs and form a setting for an exceedingly charming scene. 
The bluffs near Red Rock and Cliffland are also cut in sand- 
stone of Coal Measures age and are of interest because of their 
geological history as well as for their natural beauty. 
I have already^ spoken of the great ice-sheets and their glacial 
deposits as effacers of those types of topography which are due 
to erosion. It is partly because of this fact that the western 
two-thirds of Iowa has so few rock outcrops and hence relatively 
few spots of striking charm and beauty. Aside from a few 
Fig. 12b. Pilot Knob, Hancock county. It rises three hundred feet above 
the creek near its base. 
localities and these chiefly along the larger streams, the work 
of erosion since the retreat of the ice-sheets has been confined 
to the glacial drift deposits, which while easily eroded give rise 
to the softer, more subdued types of landscape. But there is a 
peculiar type of topography which is intimately associated with 
the depositional work of the last, the Wisconsin glacier, with the 
laying down of its load along its margin, and which consists of 
piled up mounds and intervening hollows, all without order or 
arrangement. This is known as the terminal moraine and along 
