IOWA ACADEMY OF SCIENCE 83 



area of glacial erosion. It is a part of that wide glacial delta which may 

 be compared with a continental delta, such as that which fronts our At- 

 lantic coast. The Nebraskan ice apparently overrode the rocks of Iowa 

 in the manner of a sled and not as rasp or pick, to use Chamberlin's 

 vivid metaphors. And the later ice invasions not only failed for the 

 most part to remove the ground moraines of earlier ice sheets, but they 

 also added to the pile imbricating deposits of their own. 



Addenda. In the discussion of the above paper attention was called by 

 Professor H. S. Conard and by Dr. S. W. Beyer to the fact that at Quarry 

 recent stripping had uncovered another glaciated area, and that here the 

 scorings bore to the southwest. The locality was revisited by the writer in 

 the summer of 1911. The area described was then being rapidly cut 

 away by quarrying operations. But beyond the narrow ravine which 

 bounds it on the northwest, there were found exposed two additional 

 glaciated areas, separated from each other by a narrow ravine. Here 

 the rock surface was considerably more decayed, and the glaciation less 

 complete than on the area described, but many patches of 

 sound rock were covered with well defined striae. On the middle area 

 the striae have the same general bearing as those of the southeastern area. 

 ITere a reading of S. 39° E. was noted. But on the northwestern area 

 two distinct glaciations were to be seen, each occupying its own field. 

 On the inner side, that to the northeast, the southeast glaciation was 

 found along a narrow strip about 700 feet in length, which further 

 stripping may widen. Here bearings of S. 47° E., S. 44° E., and S. 23° 

 E. were observed. The larger part of the area is occupied by patches 

 of striae bearing to the southwest. Even on surface of one or two feet 

 square these maj^ diverge as much as the following: S. 64° W., S. 53° 

 W. and S. 46° AY. Other striae whose bearings were taken had the com- 

 pass directions of S. 35° W. and S. 41° "W. The striae farthest to the 

 north bore S. 31° AV. -The two sets of striae, that of the southeast and 

 that of the southwest glaciation, approached in places as near as 10 or 

 20 feet to each other, but in only one or two doubtful cases was any 

 superposition noted. 



Since the meeting of the Academy Professor B. Shimek has generously 

 phiced at the disposal of the writer his notes on an area of glacial striae in 

 northwestern Iowa, the locality being situated two miles east of the north- 

 western corner of the state. The scorings are developed upon the surface 

 of the Sioux quartzite The prevailing direction of the striae is N. 30°-40'' 

 \V. Other crossing striae bear N. 10°-15° W. A groove eighteen inches 

 ;i cross bears N. 45° AV. and in this lay a light granite bowlder, fitting the 

 ui-oove to a nicety, but too much decayed to show planings or striae. 



