CIS GEOLOGY OF CENTRAL WISCONSIN. 



ford, DeerfieM and Rose, is a belt of greater altitude, 550 to consid- 

 erably over 600 feet above Lake Michigan. Here the lakes are less 

 abundant, the drift taking on rather the character of ridges and knolls, 

 though tortuous dry kettles are frequent. This ridge region is the 

 divide between the waters of the Fox and Wisconsin rivers, and the 

 drift depositions within it seem to have suffered little modification 

 since their first formation. The roads running eastward from Colo- 

 ma, on Burr Oak prairie, pass over parts of this great morainic heap 

 where its structure and nature are seen to great advantage. 



For further ideas as to the Kettle Range, its position, varying 

 width, and great numbers of lakes, as compared with the other parts 

 of the state, reference should be made to Plate XXYI. The lakes on 

 this plate are all, except mill ponds, that are given on the township 

 plats of the region mapped, and are accurately placed, although the 

 map is of so small scale. No doubt, others, not on the plats, occur in 

 considerable numbers. 



The materials of the drift are bowlders, gravel, sand and clay. 

 Bowlders are scattered thickly over the whole surface of the drift 

 region. Nearly all are of some sort of crystalline rock, sandstone oc- 

 curring very rarely, and limestone except as large sized pebbles 

 still more rarely. Of the crystalline rock bowlders, those of gneiss 

 of some form or other greatly predominate, making up 50 to 75 per 

 cent, of all. Next in abundance to the true gneiss bowlders, are those 

 of some form of brown-weathering, hornblendic rock, which is gen- 

 erally syenite, and nearly always gneissoid in texture. Of 80 erratics 

 counted within a few rods along the lake shore of the University farm 

 at Madison, 44 were gneiss, 15 gneissoid syenite, 9 granite, 3 diorite, 

 2 red porphyry, 2 quartzite, 2 sandstone, 1 red felsite, 1 granulite 

 and 1 fine-grained slate. Whilst other rocks are often included, these 

 numbers express, in a general way, what is true for the whole region. 

 The gneiss bowlders vary much in mineralogical composition and 

 closeness of grain, but are nearly always very distinctly laminated, 

 and often much contorted. Occasionally they run into mica slates on 

 the one hand, and gneissoid granite on the other. The granite 

 bowlders vary also, but pink orthoclase granites are most common. 

 All over the region, from Dane northward to Waushara, and prob- 

 ably far beyond, red porphyry and compact red felsite bowlders are 

 very noticeable from their bright red color, although forming only a 

 small proportion of the whole number of erratics. They include 

 kinds in which there is a compact red felsitic matrix, with dissemi- 

 nated hyaline and amygdaloidal quartz; others in which both quartz 

 and felspar are porphyritic; others in which, in addition to these, the 



