378 THE MARQUETTE IRON-BEAEING DISTEICT. 



Excelsior area. — East of tlie Dextei" iiiiiie there are again no exposures of 

 the formation for 2^ miles. However, in sees. 4, 5, and 6, T. 47 N., R. 27 W. 

 (Atlas Sheet XXV), the Negaunee belt is exposed at very numerous locali- 

 ties. The formation here has usually a somewhat regular east-west strike 

 and a soutliern dip. In a few places, especially in sec. 4, minor folds and 

 brecciation were observed. At the old Excelsior mine, just west of the 

 east line of sec. 6, the contact is again exposed between the Negaunee forma- 

 tion and the Goodrich quartzite, and here the evidence of unconformity 

 is strong, the quartzite and slate appearing to mount upon and mantle 

 around the Negaunee strata on the east side of the pit. In these exposm-es 

 the rock is niainK' ferruginous chert. In thin section the quartz is of the 

 finely crystallized kind of the Ishpeming-Negaunee area, and thus contrasts 

 with that of the Michigamme and Spurr area. 



Lake Bancroft area. — Upou tlie soutli slopc of tlic bluff uorth of Lake Ban- 

 croft (Atlas Sheet XXVIII), and at various places in the little valley separa- 

 ting the two ridges of greenstone north of this lake, are found exposures of 

 hematitic, niagnetitic, griineritie schists. These appear to have been caught 

 in the intrusive rocks. It is interesting to note that all of the rocks here 

 found are of the griinerite-magnetite-schist variety, while the ordinary 

 phases of the formation, both to the west and to the east, are the ferrugi- 

 nous cherts and jaspers, except the griineritie and sideritic slates adjacent 

 to a greenstone a short distance east of Lake Bancroft, in the north part of 

 the city of Ishpeming. In thin section the Lake Bancroft rocks show a 

 peculiarly finely crystalline or partly ■ amorphous siliceous background. 

 Also, the larger part of the iron oxide is in the form of hematite, this being 

 due to feathering. The griinerite is stained deep-red by hematite. 



Teal Lake area. — The ucxt important exposures to the east are those of the 

 Teal Lake iron range, just south of Teal Lake (Atlas Sheets XXVII and 

 XXVIII). The interest in this locality lies in the fact that the ferruginous 

 chert of the Negaunee formation rests directly upon the Siamo slate. As 

 has been said, the uppermost horizon of the latter formation is here a slaty 

 gray wacke, or a rock approaching a ferruginous quartzite. At many places 

 the change from the slate to the iron formation is sudden, the clean ore or 

 the ferruginous chert resting upon the ferruginous slate or graywacke with 



