Reviews 



SUMMARIES OF CURRENT NORTH AMERICAN PRE-CAM- 

 BRIAN LITERATURE. 



Winchell 1 discusses the general structural geologvof northeastern 

 Minnesota. The ancient rocks of this area he places in two main 

 systems, the Archean and the Taconic. The former is further sub- 

 divided into the Upper and Lower Keewatin, separated from each 

 other by an unconformity. The Pewabic quartzite also is placed with 

 the Keewatin, but is not assigned to either of the main divisions. 

 Overlying the Archean with strong unconformity is the Taconic, repre- 

 sented by Animikie and Keweenawan rocks, these divisions being sup- 

 posed to represent respectively the Lower and Middle Cambrian of 

 other parts of the country. The Coutchiching and Laurentian rocks 

 before mapped as separate formations are now included within the 

 Keewatin. 



The Lower Keewatin comprises greenstone, with associated sur- 

 face volcanics which are both subaerial and subaqueous, argyllitic 

 slates, siliceous schists, quartzites, arkoses, "greenwackes," iron ores, 

 and marble. 



•The Geology of Minnesota, by N. H. Winchell, U. S. Grant, James E. 

 Todd, Warren Upham, and H. V. Winchell : Final Rept. of the Geol. and Nat. 

 Hist. Surv. of Minnesota, Vol. IV, 1899, pp. 630. With thirty-one geological plates. 



Structural geology of Minnesota, by N. H. Winchell : Final Rept. Geol. and 

 Nat. Hist. Surv. of Minnesota, Vol. V, 1900, pp. 1-80, 972-1000. 



The first of these volumes contains an account of detailed field work Ui north- 

 eastern Minnesota, with incidental discussion of general problems. The area is 

 treated by counties and smaller arbitrary geographical divisions, in the description of 

 which several men have taken part. This manner of treatment leads to repetition in 

 the discussion of the general geological features, and in many cases it is extremely 

 difficult to correlate the facts recorded in the different sections. 



Volume V contains an account of the general structural geology of the state by 

 Professor Winchell based on the detailed work described in Vol. IV. This general 

 discussion of Vol. V is reviewed, with such reference to the facts recorded in Vol. IV 

 as is necessary to make the summary intelligible. 



Dr. Grant's views, as indicated in the detailed descriptions of special areas, in 

 some cases differ somewhat widely from those of Professor Winchell. 



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