TOPOGRAPHY. 333 



small rock masses like Michigamme Momitaiii, Avliich is composed of mate- 

 rial that offers a most stubborn resistance to all degrading agents, reach an 

 elevation of 100 to 200 feet above the general level of the surrounding 

 country. The fact that the name "mountain" has been applied to hillocks 

 of this order by the surveyors and woodsmen, who have the widest knowl- 

 edge of the Upper Peninsula, coiiveys perhaps the clearest idea of the 

 generally level character of the surface. 



While the details of the topography are thus inainly glacial in origin, 

 the broader features of the next order of importance have often clearly 

 been determined by the presence of the more resistant rocks. The large 

 structural domes of the Archean, which are such characteristic geological 

 features, are also indicated by a general upward swell of the surface of the 

 areas which they occupy. The topographical transitions at the margins of 

 these swells are frequently abrupt, and sometimes for considerable distances 

 are marked by scarp-like slopes in the granites, caused by the almost ver- 

 tical contacts with the softer Algonkian formations. Considerable portions 

 of all three of the Archean ovals in the northern part of the district display 

 this slight topographical prominence. Marginal scarps are particularly well 

 shown in the oval west of Republic, in sees. 19 and 30, T. 47 N., R. 30 W., 

 and along the south side of the oval which lies between the Fence and 

 Deer rivers, near their junctions with the Michigamme. T'he more im^jor- 

 tant bodies of greenstone also are generally expressed by a noticeable degree 

 of elevation. Thus the great intruded sheets folded in with the Lower Mar- 

 quette series in sees. 24, 25, and 36, T. 47 N., R. 31 W., give rise to long 

 broad ridges that closely follow the changes in the strike. But in all these 

 cases the topographical emphasis is very slight, and the plain as a whole 

 may truly be said to maintain its genei'al slope with practical indifference 

 to the weather-resisting differences in the imderlying rocks. 



These broader swells of the harder rocks are separated by broad, 

 slightly lower-lying plains, in many of which a valley character is still dis- 

 tinctly recognizable in spite of the fact that they especially have been 

 favored with deposits of modified drift. The present drainage, in its main 

 lines, largely follows these older valleys, although much confusion, which 

 is especially noticeable in the details, has of course resulted from their 

 partial choking by the drift. 



