298 THE MARQUETTE IBON-BBARmG DISTRICT. 



quartzite is a newer formation wliicli lia.s derived its detritus in largest 

 measure from the underlying formation. West of sec. 25 only one con- 

 tact between the granite and quartzite has been discovered, but the latter 

 near the granite at a number of j^laces becomes feldspathic in character, 

 indicating the derivation oi its material largely from the subjacent granite. 



The southern belt of the Ajibik quartzite rests unconformably upon the 

 Archean south of the Cascade range, as shown by the presence of great 

 basal conglomerates, the bowlders of which are derived from the immedi- 

 ately subjacent iron formation. The only actual contact here found is in 

 sec. 35 (see p. 311). As first observed by Wadsworth, the great conglom- 

 erate adjacent to the Piatt mine, sec. 32, T. 47 N., R. 26 W. (Atlas Sheet 

 XXXII), containing pebbles of granite, l)asic eruptive rocks, and schists, 

 each identical with the corresponding kind of rock in the Archean to the 

 south, proves tlie existence of this unconformity. Exactly similar phe- 

 nomena are found in sec. 34 (Atlas Sheet XXXV), and here the interval 

 separating the basal conglomerate and granite is but a few paces. In sec. 28, 

 T. 47 N., R. 27 W. (Atlas Sheet XXVI), the movements were so great that 

 the conglomeratic quartzite Avhich here occurs was changed into a schist. 



The contact relations of the Ajibik quartzite and the Archean seen 

 at various localities strongly suggest that in many cases which have been 

 explained as downward gradation by metaraorphism of a sedimentary into 

 a completeh' crystalline rock, or as sedimentary rock intruded lay granite, 

 the phenomena may have another explanation. If the metamorphisni in the 

 Marquette district had been so severe as to obliterate the conglomerates 

 which occur at various places, it would have been almost impossible to 

 show that between the Lower IMarquette series and the Archean there is a 

 great unconformity. 



For the southern belt the overlying formation is the Negaunee, and the 

 Ajibik quartzite or conglomerate grades into this formation by interstratifi- 

 ication, there being in some cases a number of distinctly interstratified beds 

 of quartzite or conglomerate and jasper, but always in passing to higher 

 horizons the jasper becomes predominant and tlie fragmental material of the 

 Ajibik formation disappears. In the northeast part of sec. 28, T. 47 N., 

 R. 27 W., an exceptional transition phase is a ferruginous mica-slate. The 



