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University of California Publications in Geology [Vol. 10 



the original Animikie area, since these rocks may be observed in four 

 of the districts resting on the eroded surface of the granite in rela- 

 tions so clear that they have never been questioned. In the Rainy 

 Lake and Steeprock Lake Districts the Animikian is absent. 



There is no room for doubt, therefore, that on the northwest side of 

 Lake Superior the Algoman granite was formed within the space of 

 time between the close of the Seine Epoch and the beginning of the 

 Animikian. It is highly probable on the basis of areal continuity 

 that in all the districts the Algoman granite is the manifestation of 

 one and the same general disturbance and batholithic invasion of the 

 earth's crust. The assumption that this is so is involved in the use of 

 the term Algoman as a designation for these rocks considered as a con- 

 stituent part of the earth's crust and in the use of the same term as 

 a designation for a subdivision of geological time. 



From the foregoing discussion it is apparent that the Laurentian 

 and Algoman granites afford us two splendid datum planes along 

 which we may correlate from district to district with a confidence pro- 

 portionate to the validity of the hypothesis of a definite proper age for 

 each granite. In the correlation table columns I to VI, representing 

 the sequences in the different districts, are placed side by side with 

 the granites arranged each on a horizontal line. The correlation thus 

 suggested is that which is generally accepted for the non-plutonic for- 

 mations of the pre-Cambrian of the northwest side of Lake Superior. 



South of Lake Superior. — On the south side of Lake Superior four 

 of the more important and best-known districts, namely, Gogebic, 

 Crystal Falls, Menominee, and Marquette, have been selected for con- 

 sideration in the correlation table. In each of these districts there is 

 found a group of formations comprising a basal quartzite and an 

 overlying dolomite. In the Gogebic district these are known as the 

 Sunday quartzite and the Bad River dolomite, in the Crystal Falls 

 and Menominee districts as the Sturgeon quartzite and the Randville 

 dolomite, and in the Marquette district as the Mesnard quartzite and 

 the Kona dolomite. All the geologists who have studied these districts 

 are now agreed as to the identity of this pair of formations in all four 

 districts and their correlation is not questioned. The quartzite and 

 dolomite, by whatever local name known, together represent a definite 

 stratigraphic horizon and a definite period of time. Now the quartzite 

 in all four districts rests with a basal conglomerate upon the eroded 

 surface of granite-gneiss which has been referred to the Laurentian, 

 or upon the Keewatin into which the latter is intrusive. It is there- 



