80 IOWA ACADEMY OF SCIENCE 



were shallow, and these surrounded pipes opened by ground water along 

 joint planes. Here the granular limestone was slightly decayed and re- 

 sistant crystalline shells of brachiopods were left in relief. These de- 

 pressions may be assumed to be post-glacial, since any preglacial hollows 

 as shallow as these would have been scoured as clean of all decayed rock 

 as are the surrounding levels. 



Over all this exceptionally large area only one set of striae was 

 developed. None were noted which deviated more than one or two 

 degrees from the uniform bearing of S. 22° E. ) corrected). Besides the 

 striae shallow grooves, some reaching a width of three quarters of an 

 inch are not uncommon. One of these grooves measured 18 feet in 

 length. 



The movement of the ice was clearly to the southeast. The area is 

 demarked on the northwest by a steep ravine. Here are found stoss 

 abrasion surfaces rising to the general level from one and one-half feet 

 below it. Small cavities show on the southeast side the characteristic 

 rounding of the edge, while the northwest side retains the initial profile. 

 Many examples of chatter marks were noted which were concave to the 

 southeast. 



A number of boulders lay on the glaciated surface. The largest, four 

 feet in diameter, of gray granite, was glaciated on one side. Two others 

 were distinctly faceted and scored. One, of reddish gneiss, and strongly 

 unequiaxed, (its diameter being 5, 1% and II/2 feet) lay with its long 

 axis parallel with the strife of the glaciated area. 



