THE GLACIAL DRIFT. 625 



Of the total amount of the drift materials, it is difficult to make 

 a satisfactory estimate, since the thickness is so very variable. The 

 greatest amount of material appears to be in the region of the Kettle 

 Range, and especially in that part of it that occupies Waushara and 

 the adjoining counties. Wells in the town of Oasis, Waushara county, 

 are sunk 140 to 150 feet, without striking rock. The drift hills of the 

 Devil's Lake gorge, described a short distance back, are fully 200 feet 

 thick, and may reach 300. The drift hill on the University grounds, 

 Madison, where the President's house stands, is 107 feet thick to the 

 lake level, 122 feet to rock. The Artesian well at the Capitol Park, 

 Madison, is 180 feet in drift. But the distinctly stratified drift has 

 often also a considerable thickness. It is frequently the case that in 

 valleys, wells sunk close to the rocky side hills will pass through 50 to 

 100 feet of stratified gravel, sand and clay. Nearly all the valleys have 

 their rock bottoms far below their present surfaces, whilst there are 

 even evidences of entirely obliterated valleys. On the high prairie 

 of Arlington, which is nearly everywhere underlaid, at a shallow 

 depth, by the Lower Magnesian, wells sunk within a few rods of a 

 ledge of St. Peters sandstone, on the S. E. qr., Sec. 28, pass through 

 over 100 feet of loose materials. Even on the summit of the divid- 

 ing ridge between Black and Yellow rivers, apparently stratified drift 

 has a thickness of over 100 feet. In all of the drift-bearing region, 

 wells commonly pass through 10 to 15 feet of drift-before striking 

 rock, and it is probably far within the truth to say that the drift 

 materials are equal to a layer 50 to 60 feet thick, spread over the 

 whole drift-bearing area. 



Three kinds of evidence are available with regard to the directions 

 of the glacial movement: the courses of the strise and grooves on 

 the underlying rocks; the directions of the lines of glacial erosion; 

 and the directions of travel of erratics of known origin. 



The rocks underlying the drift quite often show polishing, 

 since, and grooves, but these markings have not remained over a 

 large portion of the region, either on account of the exceedingly 

 friable nature of the rock on which they have been made, or, if the 

 rock be limestone, because this has suffered from the dissolving action 

 of carbonated water. Moreover, over great areas, the drift conceals 

 the rock basement. The markings observed are most commonly on 

 limestone, which is frequently planed and scratched in a beautiful 

 manner. One observation only has been made on sandstone, and this 

 where the sandstone was unusually hard. The only Archaean rocks 

 on which the markings have been observed, are those of some of the 

 isolated areas within the region of the Potsdam sandstone. In the 

 Wis. SUB. 40, 



