934 GEOLOGY OF EASTERN WISCONSIN. 



the depressions filled up or excavated deeper, according to tlieir na- 

 ture. The irregularities of the Kettle Range in particular are grad- 

 ually losing their conspicuous peculiarities under the gnawings of the 

 "tooth of time." The erosion of the later lacustrine and beach de- 

 posits under favorable circumstances is very rapid. We were fortun- 

 ate enough to secure reliable data in a striking instance of this kind 

 near Racine. The eroding agency is a small rivulet that is usually 

 dry a portion of the year. Twenty-eight years ago, according to Dr. 

 Hoy and others, it was the merest ditch across which two logs and a 

 few puncheons formed a rude bridge. A resident informed me that 

 two years earlier he was accustomed to drive across it without diffi- 

 culty, no bridge having been constructed al that time. At the point 

 where the bridge is now located, farther up the stream, the lake hay- 

 ing cut away the lower portion, the ditch which has been excavated ia 

 120 feet across the top, 4:0 feet deep, and 23 feet across the bottom. 



.Farther up the stream, a distance of 1,350 feet, the channel is 40 

 feet across the top, 16 feet deep and 15 feet across the bottom. It 

 is still a considerable trench at 2,750 feet from its mouth. Through- 

 out it is remarkably uniform in character and direct in course. A 

 very cautious and safe calculation shows the material removed to have 

 exceeded 2,600,000 cubic feet, or more than 3,400 cubic yards per 

 year. It is situated in a level country and does not seem to have 

 been much assisted by freshets. 



The upper portion of the material excavated is sand and gravel, an 

 ancient beach deposit, the lower portion chiefly clay. From the sur- 

 face of this clay numerous little springs seep forth and moisten the 

 sides which slide down to the bottom as soon as they are in the least 

 undermined, and the stream is thus constantly fed with silt. These 

 peculiar conditions might seem to be exceptional, but they are really 

 quite common in the lake border region. The loss from lake erosion 

 is vastly increased by the action of springs similarly situated in the 

 banks facing it. In general it may be said that the erosion of these 

 later deposits, especially of the red clays and the beach deposits, is 

 unusually rapid. 



INDUSTRIAL VALUE OF THE DRIFT FORMATIONS. 



By far the most important resource springing from the drift of 

 this region has already received consideration. I refer to our fertile 

 and enduring soils. The powdering and commingling of such a vast 

 variety of minerals by the glacial forces was a process than \vhich 

 none could be better suited to produce a secure and permanent foun- 



