emmons.] CHICAGO TO THE MISSISSIPPI RIVER. 301 



From Columbus to Rio is ground moraine, underlain by Lower 

 Mngnesian limestone, and from Rio to Portage, drift, underlain by 

 Potsdam (Cambrian) sandstone. At Portage the Wisconsin River is 

 reached, and it is followed to Kilbourn City, through Potsdam sand 

 stone, overlain by drift, -lust before Kilbourn City is reached the 

 moraine formed at the western margin of the Green Bay glacier is 

 crossed. At Kilbourn City the railway crosses the river at about the 

 center of that portion of its valley known as the Dalles of the Wisconsin. 

 The river here flows through a canyon-like gorge, 50 or 00 feet deep, 

 carved out of the Potsdam sandstone. The tributaries to the Wiscon- 

 sin in this pari of its course have cut for themselves dee]) gorges and 

 glens leading down to the main stream. From the railway line near 

 Kilbourn City may be seen isolated elevations of Potsdam sandstone. 

 which represent erosion remnants of the once more extensive Potsdam 

 formation. 



Kilbourn City to Camp Douglas. Crossing the river at Kilbourn 

 City, the driftless area 26 is entered. The sharp erosion forms, the 

 absence of drift topography, and the frequency of rock exposures com- 

 bine to place this region in sharp contrast to that farther east. In the 

 vicinity of Mauston, New Lisbon, and Camp Douglas fine castellated out- 

 liers of Potsdam Sandstone may be seen resting on a lower and often 

 nearly level plain of the same formation. 



Camp Douglas to Sparta. Between these stations the Potsdam 

 sandstone is the only formation which appears. The divide between 

 the Wisconsin and the Mississippi is here crossed, and from the sum- 

 mit the topography of the driftless area may be well seen. 



From Sparta to La Crosse the route lies in the valley of the Pa 

 Crosse river. The valley is carved from the Potsdam sandstone, 

 which forms the bluffs on either hand. In the lower part of the valley 

 the summits of the bluffs are capped with lower Magnesias limestone. 

 Loess also occurs on the summits of the bluffs fronting the Mississippi, 

 and on the bluffs bounding the La Crosse valley, near its junction with 

 the Mississippi. 



