CURRENT PRE-CAMBRIAN LITERATURE 747 
The rocks of the district have yielded to the folding in different 
ways. Where brittle the close plications have ‘resulted in their being 
fractured through and through, and in many places they pass into rei- 
bungsbreccias. ‘These phenomena are particularly prevalent in the 
Negaunee iron formation and in the quartzites. ‘The more plastic for- 
mations have yielded without major fracturing, but in a minor way 
they show everywhere the effects of deformation. A microscopical 
study shows that not a cubic inch of material has escaped dynamic 
action. While, as a further consequence of dynamic action there has 
been local faulting at various places, with two or three exceptions, no 
important faults have been observed in this district. : 
Because of the varying strength and texture of the various beds 
and formations, the readjustments necessary in folding took place 
in large measure between the different formations and between dis- 
similar beds of each formation. As these layers were rubbed over one 
another, schistosity was developed parallel to the bedding in many 
places. The unconformable contacts between the Upper Marquette 
and Lower Marquette series, and between the Archean and Lower 
Marquette series, were the greatest planes of movement, and adjacent 
to them the rocks of both the series were rendered schistose. In the 
nearly homogeneous Michigamme and other slates there apparently 
occurred an actual flowage. Here there is frequently a discordance 
between the cleavage or schistosity and the bedding. 
It is inferred from the phenomena of deformation that, when 
folded, the rocks which are now at the surface were buried under a 
thickness of several thousand feet of sediments, not impossibly as much 
as ten thousand feet. On the other hand, it appears that the forma- 
tions were not so deeply buried as to be beyond the sustaining strength 
of strong rocks like quartzites, or else the layers of these rocks would 
have been folded without the production of reibungsbreccias, as in the 
case of the Doe River quartzite of Tennessee. 
As shown by the above facts, the Marquette district furnishes a 
beautiful instance of deformation in the lower part of the zone of com- 
bined fracture and flowage.* 
The Lower Marquette and Upper Marquette series are correlated 
with the Lower Huronian and Upper Huronian series of the north 
shore of Lake Huron. ‘The reasons are stated in previous publica- 
‘Principles of North American Pre-Cambrian geology, by C. R. VAN Hise. 
16th Annual Report U. S. Geol. Surv., Part I, 1896, pp. 601-603. 
