564 REVIEWS 



reappear, with some revision, and many new data, gathered since the 

 pubhcation of the earHer volume, are incorporated. The volume is thus 

 brought up to date. Those who had reason to know the value of the first 

 volume will welcome the revision. 



The preface also announces a forthcoming volume, to be published 

 probably in 1905, on the clays, limestones, and building-stones of West 

 Virginia, to be prepared by Professor G. P. Grimsley. 



R. D. S. 



Barahoo Iron-Bearing District. (Bulletin XIII, Wisconsin Geo- 

 logical Survey.) By Samuel Weidman, Ph.D. Pp. x-f 190; 

 23 plates. 



This volume gives an account of the geology of the region about Bara- 

 boo, dealing especially with the pre-Cambrian formations in which the 

 iron ore occurs, and with the iron ore itself. This ore, it may be noted, 

 has but recently been opened up. 



The oldest rocks of the region are igneous, and include rhyohte, granite, 

 and diorite. They appear in small isolated areas only. The sedimentary 

 pre-Cambrian formations are three — namely, (i) the Baraboo quartzite, 

 3,000 to 5,000 feet thick, at the base; (2) the Seeley slate having a probable 

 thickness of 500 feet or more; and (3) the Freedom formation (dolomite 

 and iron-bearing), with a thickness of 400 or 500 feet. The iron ore is 

 in the lower part of the Freedom formation. These formations are regarded 

 as Middle or Upper Huronian. The author's statements on this point 

 are (i) that the Baraboo series is probably the equivalent of the upper- 

 most series of pre-Cambrian sediments in north central Wisconsin (p. 169); 

 and (2) "if the Huronian system, instead of consisting of two series .... 

 really consists of three unconformable sedimentary series .... then it 

 seems to the writer that the Baraboo series is, with little doubt, either 

 Middle Huronian or Upper Huronian, and more probably the former than 

 the latter." Exact correlation of the iron-ore bed with the other iron-ore 

 beds of the pre-Cambrian is not attempted. 



The ore is associated with ferruginous slate, ferruginous chert, and 

 ferruginous dolomite, and there are gradations from the ore to each of 

 these rocks. The association of the ore with dolomite is believed to be 

 unique among the pre-Cambrian iron districts of the United States. The 

 ore is mainly red hematite, with a small amount of hydrated hematite. It 

 is commonly "more like the hard phases of ore in the old ranges of the 

 Lake Superior district than the soft hydrated ore of the Mesabi district. 

 . . . . The ore is usually of Bessemer grade." 



