186 



GEOLOGY. 



kean beds are still shales, sandstones, and conglomerates in some places, 

 profound changes during the deformation which followed their depo- 





Fig. 68. Fig. 69. 



Fig. 68. — Map of a small arer, in ^he Penokee-Gogebic region of Northern Michigan, a 

 region of important iron mines. 



Fig. 69. — Section along the line Ab of Fig. 68. Shows the relation of the Animikean 

 beds to the Archean in the Penokee-Gogebic region. JR % Archean granite, Aup 

 (Palms formation), Aui (Ironwood formation [iron-bearing]), and Aut (Tyler slate) 

 are Animikean formations. Ak, Keweenawan formation. Length of section, 3| 

 miles. (Van Hise, 21st Ann. Rept., Pt. Ill, U. S. Geol. Surv.) 



sition, or subsequent to it, have affected them in others, converting 

 these common sorts of sedimentary rock into slates, schists, etc. 



Distribution. — The Animikean rocks are most commonly found 

 at the surface either about the borders of the Archean or the Huronian, 

 though isolated areas of them, not in surface association with older 

 formations, are known at a few points (south-central Wisconsin, souths 

 western Minnesota, and southeastern South Dakota, etc.; Fig. 38). 

 Their exposed parts do not, as a rule, constitute large areas, but their 

 real extent beneath other formations is doubtless great. Their original 

 extent was as great as that of the areas of sedimentation during the 

 Animikean period, and their present extent must be the same, less the 

 area whence they have been removed by erosion. 



The following sections of the Animikean in selected localities where 

 the series has been studied in detail, give some idea of its range: 



Sections of the Animikean. — In the Marquette l region, the Animikean (Upper 

 Marquette series) is unconformable on the Archean and Huronian, and is 

 divided into three formations: (1) the Ishpeming at the base, (2) the Michi- 

 gamme, and (3) the Clarksburg. The Ishpeming formation is chiefly quartzite, 

 with a basal conglomerate, but it also includes banded magnetite -griine rite 

 schist. Its thickness is 1550 feet and less. The Michigamme formation was 



1 Van Hise, 15th Ann. Rept., U. S. Geol. Surv., and Van Hise, Bayley and Smyth, 

 Mono. XXVIII, U. S. Geol. Surv. 



