STRUCTURAL GEOLOGY. 15 



The Lower Ketnvatin.) 



possible to affirm that the Upper Keewatin occurs in Minnesota in the Rainy Lake 

 region except at one point, viz., about the head of Jackfish bay, about six miles east 

 of Koochiching. The gold deposits of Rainy lake are in the Lower Keewatin. Between 

 Rainy lake and Kabetogama and Namekan lakes mica schists prevail. 



This wide belt of recrystallized fragmentals of the Lower Keewatin probably 

 underlies the most of the central and southwestern part of the state as far as to the 

 Minnesota river, which they cross with a strike nearly at right angles and with a 

 prevalent dip toward the southeast. They run below the later formations in the 

 southwestern counties, but probably occupy, with more or less of intrusive granite, a 

 wide patch in South Dakota. However, in this direction they become covered, both 

 in South Dakota and in Minnesota, by beds of Cretaceous age. 



On the south side of the Giant's range of granite, these rocks appear, and here 

 they also carry the same kind of jaspilyte iron ore, but, as the gabbro of that part of 

 the state and the Animikie strata hide them toward the east, and the drift deposits 

 of the St. Louis valley toward the west, their characters and geographic boundaries 

 are mostly unknown. They appear in the central and western portions of Carlton 

 county where their line of separation from the Upper Keewatin is quite obscure. 

 They extend southwestwardly to the central and western portions of Morrison county. 



The basic Lower Keewatin or Kawishiwin series of rocks is presumed to be of 

 very wide extent, and perhaps represents the universal original crust of the earth. 

 Its modified elastics and the still later Lower Keewatin graywackes, etc., may be 

 parallelized with some of the gneisses and mica schists which have been included 

 under the terms Laurentian and Coutchiching. 



The Lower Keewatin was terminated by an extensive folding and metamorphism, 

 and this movement was accompanied by the oldest known granitic intrusions. These 

 igneous rocks will be considered more in detail at another place, but it is germane 

 to state here that these granitic areas rise as bosses in the midst of the older schists 

 and also penetrate the later greenstones and their attendants as dikes. They vary 

 from indefinite felsitic rocks to quartz-porphyry arid to aplitic granite, as dikes, and 

 to coarse granite in larger areas. There are also some indications that some basic 

 rocks of igneous character and intrusive structure date from the Lower Keewatin. 

 Such are certain altered gabbros. The only known occurrences of an Archean gabbro 

 in Minnesota are at a few miles southwest from Motley, in Todd county, and at 

 Little Falls, in Morrison county. There is also an important area of gabbro at Knife 

 lake, on the international boundary, along the southeastern shore, but it is probably 

 of more recent date than the Lower Keewatin. By far the larger part of the granites 

 of the state date from the close of the Lower Keewatin. Such are the granites of 

 Bassimenan lake, of Saganaga lake, a part at least of the Giant's range, and of the 



