ELY GREEN J^TONE. 149 



area several liundred paces long. In the center of this large exposure the 

 ellipsoids are relatively little mashed, and show the aphernlitic structure 

 within them as well as the matrix between them. This was evidently a 

 part of the rock mass that acted as a buttress, and was not afiFected by the 

 mashing, as was the rock on each side of it. On the sides of the ridge the 

 ellipsoids are much flattened. The rock in places passes into a greenstone- 

 schist in which the ellipsoidal structure is totally obliterated. Between 

 these green schists on the one hand and the typical ellipsoidal greenstone 

 on the other there are various gradations. The intermediate phases show 

 a certain coarse banding which, by a careless observer, might be mistaken 

 for lines of sedimentation. This banding is produced in the way indicated 

 above, the bands being of two kinds, one kind produced from the matrix 

 and the other produced from the original ellipsoids. 



Still another excellent exaixiple of this pseudobedded structure may 

 be seen in the Archean just north of the railroad near the east end of the 

 place where the Duluth, Port Arthur and Western Railroad first reaches 

 the shore of Gunflint Lake from the east. This is north of the railroad 

 track and distant from it from 75 to 150 paces. To the north the green- 

 stone is fairly massive, and in places is distinctly ellipsoidal. Toward the* 

 south, nearer the overlying sedimentaries and consequently nearest the 

 plane along which movement must have taken place during the folding of 

 the rocks, it becomes decidedly schistose. The ellipsoidal masses are 

 flattened to such an extent as to give a I'ough banding to the rock. 



This description of the ellipsoidal structure in these greenstones would 

 not be complete if attention were not called to the frequency of its occur- 

 rence' in the various districts of the Lake Superior region. Thus, for 

 example, it has been described from the Marquette and the Crystal Falls, 

 districts of Michigan, and one can state with a fair degree of assurance,, 

 from the occurrence of large quantities of greenstones in the Penokee- 

 Gogebic of Michigan and Wisconsin, that it also occurs there, although it 

 has not been described from that district. It has also been observed by the 

 writer in a number of places in the Menominee district of Michigan and in 

 the Mesabi district of Minnesota. Lawson describes it in the rocks of 

 the Lake of the Woods region." The same structure has been described 



"Geology of the Lake of the AVoods region, by A. 0. Lawson: Geol. and Nat. Hi.st. Survey of 

 Canada, 1885, pp. 51-53cc. 



