192 C. K. LEITH 



Basal Sandstone including the sandstone and shale series between the 

 Keweenawan and the St. Lawrence shales." 



Winchell 1 discusses the significance of the fragmental eruptive 

 debris at Taylor's Falls, Minn. This has heretofore been regarded as 

 a conglomerate resting unconformably upon the Keweenawan. As a 

 result of recent field work by Mr. C. P. Berkey, it is believed that this 

 conglomerate may be separated into two conglomerates, an upper one 

 at the base of the upper division of the Cambrian, and a lower one at 

 the base of the lower division. The latter would come within the 

 Keweenawan, as this term is used by Irving and other writers, and 

 would separate this series into two parts. 2 The later conglomerate 

 rests directly upon the earlier one, leading to the previous confusion 

 of the true relations. Similar conglomerates found in the Keweenawan 

 at several points between Duluth and Grand Portage have led to 

 the conclusion that the Keweenawan may be divided into two great 

 series, separated by conglomerate and quartzite which reach a thickness 

 of several hundred feet. The lower series has been included in .the 

 Norian, and the upper series comprising the sedimentaries and the 

 eruptives above them, has been called Keweenawan, the Keweenawan 

 forming the lower division of the Cambrian. 



Cofnments. — While the conglomerate within the Keweenawan at 

 this locality has not before been noted, the occurrence of many con- 

 glomerates at other localities in the middle and upper part of the 

 Keweenawan has been mapped and described by the Michigan and 

 United States geologists, as a glance at Marvin's Eagle River section 3 

 and Irving's general report 4 on the Keweenawan will indicate. Instead 

 of one conglomerate, there are a dozen conglomerates at different hori- 

 zons. However, these conglomerates are composed almost without 

 exception of local material, derived wholly from contemporaneous 

 lava flows, and are held to mark very insignificant breaks in the series. 

 As seen from Winchell's description, the Taylor's Falls conglomerate 

 belongs to this class. The United States geologists, recognizing the 



1 The significance of the fragmental eruptive debris at Taylor's Falls, Minn., by 

 N. H. Winchell: Am. Geol., Vol. XXII, 1898, pp. 72-78. 



2 In a recent paper, above summarized, Mr. Berkey (Am. Geol., Vol. XX, p. 381) 

 takes the view that the lower conglomerate is a flow breccia of the igneous rocks. 



3 Geology of Michigan, 1873, Vol. I, Part II, Copper-bearing rocks, pp. 1 17-140. 



4 Copper-bearing rocks of Lake Superior, Mon. V, U. S. Geol. Surv., 1883. 



