188 



GEOLOGY. 



schists, ferruginous cherts, actinolite and griinerite schists, and iron ore are 

 included in the formation. The sedimentary beds are affected by dikes, the 

 rocks of which range from acid to ultra-basic. The thickness of the formation 

 is about 2000 feet. 



Fig. 71. — Map showing the surface relations of Archean, Huronian, and Animikean 

 formations in a small area in northern Michigan. JRqr, Archean granite; Ala 

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

 Huronian formations. Aui (Ishpeming formation) and Awn (Michigamme forma- 

 tion) are Animikean formations. Aed, eruptive diabase or diorite. Length of 

 area, 3 miles. (Van Hise, Bayley, and Smyth, U. S. Geol. Surv.) 



In the Penokee-Gogebic region of Wisconsin and Michigan, 1 the Animikean 

 consists of (1) the Palms formation below, a quartz slate formation, with basal 

 conglomerate, resting unconformably on the Huronian or the Archean, and 





Fig. 72. — Section along the line Ab of Fig. 71. 



having a thickness of 300-800 feet; (2) the Ironwood formation, consisting of 

 (a) cherty iron carbonate, (6) ferruginous slates and cherts, and (c) actinolitic 

 and magnetitic slates. The cherty iron carbonate represents the original con- 



1 Van Hise, 10th and 21st Ann. Repts., IT. S. Geol. Surv.; Irving and Van Hise, 

 Mono. XIX, U. S. Geol. Surv. 



