78 IOWA ACADEMY OF SCIENCES. 



devoted solely to pasture. Wells show that the floor of this 

 valley is made up of sand and gravel. The water supply for 

 the town of Wall Lake is obtained from a well fourteen feet 

 deep, in this hollow. The supply is abundant, the well filling 

 as fast as the water is pumped out. The Lake View gravel 

 pit extends for a mile along the west side of this hollow. It is 

 operated by the Chicago & North- Western railroad, and yields 

 great quantities of excellent ballast. The area already exca- 

 vated, added to that which has been prospected and stripped, 

 shows that the width of the deposit is at least a fourth of a 

 mile. It probably extends along the hollow till it swings to 

 the west. The material is a uniform grade of sand and gravel, 

 at least 15 feet thick. Everywhere the deposit shows oblique 

 lamination. In the finer material quartz abounds, while in 

 the coarse limestone predominates. All of the rock fragments 

 are water worn and rounded. A section 10 feet in height 

 shows that the material is evenly sorted from top to bottom. 

 The railroad is operating the pit on an extensive scale. 



At present Wall lake is drained by the 'Coon river. The 

 little stream connecting them has no valley, nor can it be said 

 to have made a course of its own. It is connected with the 

 east end of the lake, and the region just east of the lake 

 through which it flows is lower than the lake itself. Thus is 

 brought about the curious condition that White describes, of a 

 lake lying in a valley which it only partly fills with a wall at 

 each end across the valley, which permits the water in the 

 lake to rise above the level of the land which is only a few 

 rode, or at some points only a few yards away at each end. 

 The stream draining the lake winds around among the morainic 

 knobs that are conspicuous at the east end of the lake, seeking 

 the lowest levels, doubling on itself till it apparently stumbles 

 into the Coon river. The hollow excavated by the stream is 

 seldom more than 30 feet wide and 6 feet deep. Beyond this 

 the stream has no effect on the topography, except at points 

 where a slightly deeper excavation was necessary to connect 

 hollows somewhat separated. Evidently the water rose in 

 the lake till it found an outlet at the east end, then filled the 

 hollow at that point till an elevation was reached sufficient 

 to permit it to flow into the hollow just beyond and so on till 

 the 'Coon river was reached, two miles away. Then the slight 

 task of cutting down the insignificant barriers between the 

 hollows was begun. The nature of the stream's course shows 



