FOLDING OF BASEMENT COMPLEX AND MARQUETTE SERIES. 571 



southeiist (|uartcr of tlic section, the Carp Rivin- Hows uloni;- tlic liiu^ of a 

 fault, the (|iiart/.it(^ formation In'inj)' displaced laterally some hundreds of 

 feet. Tlic horizontal throw is here jjerhaps more than 500 feet, but jn-ob- 

 ably less than 1,000 fci-t. How far this fault extends to the northwest and 

 southeast the outcrops arc insufficient to determine. 



It is inferred from tlu; phenomena of deformation that, when folded, the 

 rocks which are now at the surface were buried imder a thickness of several 

 thousand feet of sediments, not impossibly as much as 10,000 feet. While 

 the Upper Marquette slate has at the present time in this district no such 

 thickness as this, in the Penokee district 10,000 feet is exceeded, and it is 

 probable that this great slate formation once extended with nearly or quite 

 its full thickness over the Marquette district. On the other hand, it a])pears 

 that the formations were not so deeply buried as to be beyond the sustain- 

 ing strength of strong rocks like quartzites, or else the layers of these rocks 

 would have been folded upon themselves without the production of reibungs- 

 breccias, as in the case of the Doe River quartzite in Tennessee. Had the 

 rocks which are now exposed not been deeply covered it is hardly possil)le 

 that the complicated folding above described could have occurred without 

 complicated faulting. 



As shown by the above facts, the Marquette district furnishes a beau- 

 tiful instance of deformation in the lower part of the zone of combined 

 fracture and flowage.^ 



INTRUSIVES, 



Abundant altered diabase and other rocks were intruded in Ijoth the 

 Lower Marquette and Upper Marquette series. This is shown by bosses 

 cutting across the bedding of the layers or bei\ding them (PI. XI), by dikes 

 branching off from the bosses and cutting the formations of both the Mar- 

 quette series (PI. XXX), and by large and small inclusions of griinente-mag- 

 netite-schist in the greenstone at the Lowthian and 8i)urr mines (PI. XII). 

 The most of the intrusive greenstones are of Clarksburg or pre-Clarksburg 

 age. They particularly affect the iron-bearing fonnation of the Lower 



'Principles of North American pre-Cambriau geology, by C. R. Van Hise: Sixteenth Ann. 

 Kept. U. S. Geol. Survey, Part 1, 1896, pp. 001-603. 



