CHAPTER VIII. 



TOPOGRAPHY OF THE DISTRICT IN ITS RELATION TO 

 GEOLOGIC STRUCTURE. 



The relationship of topographic reUef to geologic structural features 

 is probably uowhere better brought out than in the Vermilion district. 

 From the preceding pages the reader will have learned of the gabbro 

 plateau (pp. 37, 399) with its simple topographic features due chiefly to the 

 homogeneous character of the gabbro, the country i-ock, and of the peculiar 

 topography of the sawtooth hills area (pp. 38, 391, 400) due to the presence 

 of the sills intercalated between the beds of slates with their monoclinal 

 dip to the south-southeast. The descriptions which follow apply esjDecially 

 to the broad area north-northwest of the Giants range and to the Giants 

 range itself 



In these portions of the Vermilion district the rocks are closely folded 

 into synclines and anticlines, frequently arranged en echelon, which, in 

 general, have an east-northeast trend. Moreover, the oldest rocks are the 

 hardest, and these usually occupy the anticlines; whereas the troughs are 

 occupied by the younger, softer rocks. The minor structures, such as 

 cleavage and fissility, are in general parallel with the above structural 

 arrangement. Asa consequence of the combination of these factors, which 

 are of the greatest importance in determining the topography, we find the 

 main ridges to be usually anticlines of older rock, with the intervening 

 valleys in synclines of younger and less resistant rocks. Almost without 

 exception the main ridges and valleys, and to a very great extent the minor 

 ones also, agree with the trend of the geologic structure and run east- 

 northeast. 



Beautiful examjDles of the relationship between the topography and 

 geologic structure are shown in the cases of Tower and Lee hills at Tower 

 and of Soudan Hill at Soudan. Here the anticlinal hills of resistant 



