STRATIGRAPHY. 33 



great muskegs" extend over large areas. In that region outcrops are very 

 scarce, but exposures of banded jasper andiron ore have been found associ- 

 ated with greenstones, granite, and clastic sediments. A reconnaissance 

 trip was made through it in 1886 by Mr. W. N. Merriam for the United States 

 Geological Survey, and this work, as well as that done in that portion of the 

 district for private corporations, to whose results the Survey has had access, 

 shows the futility of attempting at present to trace out formation lines in that 

 region. Hence the Survey has done no detailed work west of the above line. 



The same rocks that occur at the eastern end of the district are known to 

 continue for many miles eastward, both in the United States and in Canada. 

 Hence this eastern limit also is arbitrary, and includes, indeed, rocks that are 

 the direct eastward continuation of the topographic feature known as the Me- 

 sabi range, which in the western part of the district lies south of the Vermilion. 



The southern and northern limits are sharply defined, and are well 

 marked geologically by granite and gabbro. The gabbro bounds only the 

 southern side of the district in the eastern part. 



STRATIGRAPHY. 



The stratigraphic succession in the Vermilion district is as follows, in 

 descending oi'der : 



Pleistocene Drift. 



Keweenawan Dulutli gabbro and Logan sills. 



(Unconformit)'. ) 

 Upper Huronian (Animikie series). Con-fRove slate, 

 fined to east end of district IGunflint formation (iron-bearing). 



(Unconformity. ) 



Ilntrusives. Granites, granite-porphyries, dolerites, and 

 lamprophyres. 

 Knife Lake slates. 

 Agawa formation (iron-bearing). 

 Ogishke conglomerate. 

 ( Unconformity. ) 



Intrusive granites, granite-porphyries, and some green- 

 stones. 

 Archean J Soudan formation (the iron-bearing formation). 



~ I (Minor unconformity. ) 



Ely greenstone, an ellipsoidally parted basic igneous and 

 largely volcanic rock. 



« These muskegs, as they are called by the Indians, are great open swamps that are comparable 

 in a way with the northern tundras. They have been formed in most cases by the drying up of large 

 bodies of water, and in many of them th£re is now an open area occupied by the remnant of a larger 

 lake. Over the area surrounding the water there is spread a growth made up largely of sphagnum 

 moss, wild cranberry bushes, and other water-loving plants, with occasional swamp-growth shrubs that 

 attain a height of 1 to 3 feet. Out of this thick undergrowth there rise isolated tamarack and spruce 

 trees, usually of small size. Where these muskeg swamps border the large lakes they are sometimes 

 flooded during high water. 



MON XLV — 03 3 



