abstracts: geology 1~>7 



GEOLOGY.— The geology of the Lake Superior Region. C. R. Van 

 Htse and C. K. Leith. Monograph CJ. S. Geological Survey No. 

 52. Pp. 630, with maps, sections, and views. 1911. 



This monograph gives the first connected account of the geology of i he 

 Lake Superior region as a whole, with special reference to the iron-bear- 

 ing and copper-bearing formations. Attention is directed primarily to 

 the correlation of the formations, to the geologic history of the region, 

 and to the origin of the ores. In addition, there are brief chapters on 

 parts of the district which had not previously been reported on by the 

 United States Geological Survey. 



The Lake Superior region, comprising approximately 181,000 square 

 miles, includes three topographic provinces: (1) the peneplain of the 

 Lake Superior highlands; (2) a series of lowland plains surrounding 

 the peneplain on the east, south, and west; and (3) the deep basin of 

 Lake Superior. These provinces are in various stages of development 

 and preservation. 



The Pleistocene epoch is treated in four stages: (1) preglacial time, 

 when the topography was much as it is now except for certain valleys 

 that were later deepened by glacial erosion, broad areas that were after- 

 wards covered by glacial drift, and an entire contrast of drainage; (2) 

 the time of advancing glaciers, when the land was gradually being covered 

 and eroded by an ice sheet, drainage was being modified, and plants 

 and animals were being driven out; (3) the time of retreating glaciers, 

 when from an extreme stage of glaciation with only the Driftless Area 

 uncovered the present topography was revealed by the gradual melting 

 of a largely stagnant ice sheet; (4) the present stage of modification of 

 glacial deposits, building of stream and lake deposits, return of plants 

 and animals, and a general tendency toward the restoration of the con- 

 ditions that prevailed before glaciation. 



The lowest rocks found in the region are those of the Archean system 

 or basement conplex, consisting of the Keewatin and Laurent ian series. 

 These are overlain successively by the Keweenawan and Huronian series, 

 which together make up the Algonkian system. In certain districts t he 

 Huronian is separable into two or three divisions, marked by uncon- 

 formities. None of these formations is fossiliferous. The Keewatin 

 series, where relatively unchanged is remarkably uniform in character. 

 and even the metamorphosed portions show features that indicate ori- 

 ginal identity with the less altered portions. The Keewatin comprises 

 a dominant igneous formation and a subordinate sedimentary formation. 



