REVIEWS 903 



Duparc * describes the copper-bearing (Keweenawan) rocks 

 of the northwest extremity of Keweenaw Point, Michigan. The 

 article is throughout merely a summary of previous reports on 

 this area by the geologists of the Michigan and United States 

 Survey, and this moreover without a single reference to such 

 reports. 



Hall 2 describes the Keweenawan rocks south and southwest 

 from Duluth, along the St. Louis and St. Croix rivers, and shows 

 that a series of alternating lava flows and sediments lie in a 

 synclinal northeast-southwest trough, the western border of 

 which is marked by a profound fault. To the east of the fault 

 the Keweenawan rocks are highly tilted to the southeast, while 

 to the west of it the Cambrian rocks are much broken up. The 

 relations of the fault to the distribution of the flows and 

 analogy with other volcanic regions seem to show that the fault 

 was a plane of weakness along which most of the lavas were 

 originally erupted. The faulting was pre-Cambrian, Cambrian, 

 and post-Cambrian, as shown by the fact that in some places 

 the Cambrian rests horizontally upon the upturned Keweenawan 

 rocks, and in others is much broken up. 



Hall 3 describes and maps the slates and associated rocks in 

 the vicinity of Cloquet and Carlton on the St. Louis River, and 

 certain hornblendic and micaceous schists associated with gran- 

 ite and diabase to the west along the Mississippi and Snake 

 rivers. He maintains that the slates and graywackes to the 

 east and the hornblendic schists to the west belong to one 

 and the same series, and that the schists have resulted from the 

 metamorphism of graywacke and slate by the intrusion of 

 granite. Still later intrusions of diabase have cut both the 

 granites and the slates. Accepting Spurr's statement that 

 the Carlton slates are Keewatin or Lower Huronian, the con- 



'"Note sur la Region Cuprefere de l'extremite Nord-Est de la peninsule de 

 Keweenaw (Lac superieur)," par Louis Duparc , Archives Sci. Physique et Nat., 

 Tome X, 1900, p. 21. 



2 " Keweenawan Area of Eastern Minnesota," by C. W. Hall, Bulletin of the 

 Geological Society of America, Vol. XII, 1901, pp. 313-42, Pis. 27-28. 



3 "Keewatin Area of Eastern and Central Minnesota," by C. W. Hall, Bulletin 

 of the Geological Society of America, Vol. XII, 1901, pp. 343-76, Pis. 29-32. 



