THE ARCHEOZOIC ERA. 



149 



have been investigated in some detail. The following brief statements con- 

 cerning the rocks of the system at selected points may be supplemented by the 

 study of the original treatises referred to. 



In the Marquette region of northern Michigan, the Archean consists of (1) 

 the Keewatin, Mona, and Kitchi schists (metamorphosed lavas and tuffs), with 



<5ce.le 



Archean 



Huronian and Animikean. 



.Mil, 



Keweenawan 



wm 



Post-Algonkian 



Fig. 39. — Map of the Lake Superior region showing the distribution of Archean, 

 Huronian, Animikean, Keweenawan, and post-Proterozoic formations. (Van 

 Rise and Leith, U. S. Geol. Surv.) 



which are associated serpentines and dolomites (both derived in part from peri- 

 dotites), and (2) the Laurentian, gneissic granite and more or less syenite, intru- 

 sive in the schists. These rocks are affected by numerous dikes and bosses of 

 diabase, basalt, and granite. 1 A section showing the relations of the Archean 

 to the Proterozoic rocks in this region is given in Fig. 40. 



In the Menominee region, a little farther south, the Archean consists of (1) 



nee; Montana, Fort Benton, Little Belt, Three Forks, and Livingston; North 

 Carolina-Tennessee, Asheville and Cranberry; Tennessee-North Carolina, Greenville; 

 Wyoming, Absaroka and Yellowstone. 



1 Van Hise, 15th Ann. Rept., IT. S. Geol. Surv., pp. 517-589, and Van Hise, Bay- 

 lev and Smvth, Mono. XXVII, U. S. Geol. Surv. 



