ELY GREENSTONE. 135 



follow the low, rounded knobs or ridges of the greenstone. After passing 

 over these and ascending a gentle slope the top is reached, which is usually 

 a broad, flat dome. The descent on the other side carries one over similar 

 topography, with the topographic break intervening in most cases between 

 the greenstone and the sediments. In these large ridges the minor details 

 of the topograph}^ are usually not very strongly accentuated, but in each 

 case blend in the main ridge which, while forming a very marked topographic 

 feature, is in general not separated into distinct peaks. 



STRUCTURE. 



In view of the essentially homogeneous, igneous character of the Ely 

 greenstone, it will be readily seen that the geologic structure of the green- 

 stones areas could not have been determined without the aid of the younger 

 sedimentary formations. As the result of the study of the district, we 

 find that the greenstones have been intricately folded, the folds have in many 

 instances been carefully traced, and it has been found that in general the 

 greenstone has been folded into a great syuclinorium. The character of 

 this is better brought out in the western than in the eastern part of 

 the district. Within this synclinorium the synclines are occupied by the 

 younger rocks, whereas the anticlines are of greenstone projecting through 

 sediments of younger age. Typical anticlines of the greenstone, partially sur- 

 rounded by the sedimentaries, occur in the vicinity of Vermilion Lake, in the 

 western part of the district and are enumerated on page 432. Attention is here 

 again called to the possibility that the greenstones reported to occur west of 

 that part of the district mapped are perhaps the crest of greenstone anticlines 

 projecting through the drift. The rocks of the Vermilion district have been 

 affected by a second system of folds lying approximately at right angles to 

 those that form the great east-west trending synclinorium. The effect of 

 this cross folding is best shown by the steeply plunging anticlines and 

 synclines in the sediments of later age, as well as by the distribution of the 

 formations in general. If we examine the map including the area near the 

 west end of Moose Lake, we find that as a result of the main folding the 

 gi-eenstone has been divided into a number of narrow belts separated from 

 one another north and south by still narrower belts of sediments lying in 

 synclines between the greenstones. It will be noted, also, that some of these 

 belts are completely isolated and that others have but shght connection. 



