458 



STRATIGRAPHICAL GEOLOGY. 



Michigan. The underlying rock is the same, but it is covered by the " Copper series," 

 a group of strata devoid of fossils, and situated beneath the Lake Superior sandstone, 

 which is now commonly esteemed as the equivalent of the Potsdam. The Huronian 

 is therefore older than the fossiliferous Cambrian. 



Huronian System of Michigan. 



The latest studies in this region have been made by Messrs. Pumpelly, Brooks, and 

 Wright, and are described partly in the report upon the geology of Michigan, and 

 partly in special papers, by Major T. B. Brooks, in the American Jo7irnal of Science. 

 I accept these latest studies as the best. The system is divided into twenty parts, and 

 I give in parallel columns the specifications concerning their nature in the two best 

 known districts, Marquette and Menominee. The Huronian is said to be distinctly 

 unconformable to the Laurentian. 



'Marquette Region. 



XIX. Mica schist, with staurolite, an- 

 dalusite, and garnet ; quartz, in bunches, 

 and rare hornblende seams. 



Ouartzite, and probably soft slate. 



XVII. Anthophyllitic (?) schist, usually 

 magnetic and manganiferous. 



XVI. Banded ochrey porous quartz 

 schist. 



XV. Blackish argillaceous slate, rarely 

 micaceous, occasionally with garnets. 



XIV. Gray arenaceous quartzite ; quartz 

 conglomerate. 



XIII. Hematite and magnetic ores; 

 banded jaspery schist, and beds of chlo- 

 ritic and hydro-mica schists. 



XII. Red quartz schist, with banded mi- 

 caceous iron ; quartzose limonite ores. 



XI. Diorite, hornblende schist, chlorite 

 schist, chloritic-looking mica schist ; rare- 

 ly hornblende gneiss. 



X. Hematitic and limonitic schists, of- 

 ten manganiferous ; siliceous schists ; gar- 

 netiferous, anthophyllitic schists. 



Menominee Region. 



XX. Granite and gneiss. 



XIX. Mica schist, with staurolite and 

 hornblende schist — rarely gneiss — chlorit- 

 ic schist ; granitic dykes. 



XVIII. Quartzite, with chloritic, mica- 

 ceous, and argillaceous schists and slates. 



XVII. Chiefly hornblende schist and re- 

 lated greenstones and chloritic schist. 



XVI. Chiefly clay slate, often ferrugi- 

 nous ; also hydro-magnesian schists ; mi- 

 caceous quartz schists ; hematite schists ; 

 rarely hornblende rocks and greenstones. 



XV. Gabbro or diabase, with green- 

 stones ; ferruginous and actinolitic schists. 



XIV. Unctuous hydrous magnesian 

 schist ; sericite, quartzite, and chloritic 

 greenstones. 



XIII. Chloro-argillaceous slate, chlorit- 

 ic schist, diorite, carbonaceous slate, and 

 anthophyllitic schist. 



Hornblende rock and chlorite mica 

 schist. 



Micaceous clay slate (phyllite), with 

 seams of quartz ; carbonaceous slate. 



Whitish dolomitic marble, with 

 tals of tremolite and wollastonite. 



crys- 



