180 GEOLOGY. 



1500 feet thick; and (3) the Negaunee formation of slight development, cor- 

 responding with" the formation of the same name in the Marquette region. The 

 series is closely folded, and the beds are often vertical. 



r-£L_ Au AU^r^dh^ 



Fig. 65. — Section showing the relations of the Archean, Huronian, and Animikean at 

 one point in the Marquette (N. Mich.) region. ARgr, Archean granite; Ala (Ajibik 

 quartzite), Als (Siamo slate), and Aln (Negaunee [iron-bearing] formation) are 

 Huronian formations. Aui (Ishpeming formation) and Aum (Michigamme slate) 

 are Animikean formations. Length of section, 2 miles. (Van Hise, Bayley, and 

 Smyth, U. S. Geol. Surv.) 



In the Crystal Falls region of northern Michigan, 1 the Huronian series consists 

 of four formations. In ascending order, these are (1) the Sturgeon quartzite, (2) 

 the Randville dolomite, (3) the Negaunee formation, and (4) the Hemlock for- 

 mation. The Sturgeon quartzite has a basal conglomerate, and a thickness 

 ranging from 100 to 1000 feet. It grades into the Randville dolomite, which is 

 estimated to have a thickness of 1500 feet. The Negaunee formation is iron- 

 bearing, and is similar to the corresponding formation of the Marquette region. 

 The Hemlock formation consists principally of volcanic rocks, both acidic and 

 basic, and of crystalline schists derived from them. The Huronian rocks of this 

 region have been twice folded, the axes of the folds being nearly at right angles. 

 The rocks are notably metamorphosed. 



In the Penokee-Gogebic region (Wis.-Mich.) 2 two formations are found, a 

 quartzite (Mesnard) below, and a dolomite (Kona) above. It is unconformable on 

 the Archean, and has a monoclinal structure, the beds dipping at high angles.. 



In the Mesabi (Minn.) 3 district, the Huronian series consists of metamorphosed 

 graywackes, slates, conglomerates, and granites, unconformable on the Archean. 

 The thickness is at least 5000 feet, and may be 10,000 feet. The bedding and 

 schistose cleavage are nearly vertical. 



The Huronian of the Vermilion (Minn.) region* is made up of three conformable 

 members, (1) the Ogishkee conglomerate below, (2) the Agawa (iron-bearing) 

 formation in the middle, and (3) the Knife Lake slates above. 5 The Ogishkee 

 conglomerate is a basal conglomerate, unconformable on the Archean. The 

 Agawa formation has a carbonate, slaty facies, and a chert, jasper, iron oxide, 

 and slate facies. Lithologically, it is very like the Soudan formation of the Archean 



1 Van Hise, 21st Ann. Rept. U. S. Geol. Surv., and Van Hise, Clements, Smyth, 

 and Bayley, Mono. XXXVI, U. S. Geol. Surv. 



2 Van Hise, 10th and 21st (Pt. Ill) Ann. Repts. U. S. Geol. Surv.; also Irving 

 and Van Hise, Mono. XIX, pp. 127-142, U. S. Geol. Surv. 



3 Leith, Mono. XLIII, U. S. Geol. Surv. 



* Clements, Mono. XLV, U. S. Geol. Surv. 



5 In the latest publication touching this region, the name of the Agawa forma- 

 tion is omitted. Jour, of Geol., Vol. XIII, p. 94. 



