1 42 SALISBURY AND A TWOOD 



through what is now the Lower Narrows of the Baraboo, thence 

 through the Devil's Lake gorge to its present valley to the south. 

 If this be true, the Baraboo must at that time have joined this 

 larger stream at some point east of the city of the same name. 



Extinct glacial lake on the east quartzite bluff . — Between the arms 

 of the main terminal moraine loop on the quartzite range, about 

 two miles east of Devil's Lake, is a notable flat. Its location and 

 extent are shown in Fig. 2 (/). With the exception of the north 

 side, and a narrow opening at the northwest corner, the flat is 

 surrounded by high lands. When the ice occupied the region, 

 its edge held the position shown by the line marking the limit 

 of its advance, and constituted an ice barrier to the north. ^ The 

 area of the flat was, therefore, almost shut in, the only outlet 

 being a narrow one at h, Fig. 2. Excavations in the flat show 

 that it is covered with stratified sands, gravels, and cJays of gla- 

 cial origin, to a depth of at least sixty-five feet. If this filling 

 were removed, the bottom of the area would be much lower than 

 at present, and it is evident that when the ice had taken its 

 position along the north side of the flat, an enclosed basin must 

 have existed. Into this basin water from the melting ice flowed, 

 forming a lake. At first it had no outlet, and the water rose to 

 the level of the lowest point {Ji, Fig. 2) in the rim of the basin, 

 and thence overflowed to the west. Meanwhile the sediments 

 borne in by the glacial drainage were being deposited in the lake 

 in the form of a subaqueous overwash plain, the coarser parts 

 being left near the shore, while the finer were carried further out. 

 Continued drainage from the ice continued to bring sediment 

 into the lake, and the subaqueous overwash plain extended its 

 delta-like front farther and farther into the lake, until its basin 

 was completely filled. With the filling of the basin the lake 

 became extinct. Further drainage from the ice followed the line 

 of the outlet, the level of which corresponds with the level of 

 the filled lake basin. This little extinct lake is of interest as an 



■The moraine line on the map represents the crest of the marginal ridge rather 

 than its outer limit, which is slightly nearer the lake margin. Stratified drift of the 

 nature of overwash also intervenes at points between the moraine and the lake border. 



