98 GEOLOGY OF EASTERN WISCONSIN. 



2. The modifications of the surface constituting this first class of 

 topographical features were produced by running water, those of the 

 second class, which were produced next in order of time, were formed 

 by ice in the form of glaciers, it is confidently believed, and by the 

 agencies brought into action through their melting. The work of the 

 ice was two-fold: first, in the leveling of the surface by planing down 

 the hills and filling up the valleys; and second, in the creation of a 

 new uneven surface, by heaping up in an irregular and promiscuous 

 manner the clay, sand, gravel and bowlders it had formed, thus giving 

 the surface a new aspect. 



Among the features produced by the action of the ice, are parallel 

 ridges sometimes miles in length, having the same direction as the ice 

 movement, hills of rounded flowing contour sometimes having a lin- 

 ear arrangement in the direction of glacial progress, mounds and 

 hummocks of drift promiscuously arranged on an otherwise plane 

 surface, oval domes of rock (roches moutonees), sharp gravel ridges, 

 often having a tortuous serpentine course, transverse to the drift 

 movement, peculiar depressions known as " kettles," and half sub- 

 merged rock gorges, known as fiords, all of which will be considered 

 more fully in describing the minor topographical features of the re- 

 gion, and in discussing the Quaternary formations. 



The melting of the ice mass gave rise to swollen lakes and flooded 

 rivers, which eroded at some points and filled up at others, and so 

 still farther modified the face of the country. All these peculiarities, 

 being the result, directly or indirectly, of the ice action, may be de- 

 nominated Glacial features. 



3. Subsequent to the Glacial period, the wearing action of the 

 streams was resumed, but under somewhat new conditions. In addi- 

 tion to this, there occurred a depression 'of the land toward the north 

 of several hundred feet, attended by an increased volume of water in 

 the lakes, by which nearly one-half of the district was submerged. 

 The advancing waters of this period leveled down many of the surface 

 irregularities, and while the land was submerged the " red clay" was 

 deposited which still further leveled the surface. After the land 

 arose again from the water, the streams resumed their cutting, and as 

 the clay was soft, they rapidly eroded deep, wide gorges, leaving 

 abrupt terraces on either side. The results of the these agencies pro- 

 duced peculiarities in the surface contour that may, following out our 

 plan, be called Post-Glacial features. 



To the three agencies, lake action, ice and running water, assisted 

 slightly by winds, the topographical peculiarities of the district are 

 chiefly due. There is no evidence of violent eruptions, upheavals or 



