596 WILLIAM J. MILLER 



of the park, or during the tremendous process of thrust faulting of 

 the district, or both. 



In a discussion of the highly folded gold-bearing series of Nova 

 Scotia, Faribault^ has figured and described some interesting 

 cases of intraformational corrugated quartz veins in slate lying 

 between beds of quartzite. He says: " Inters tratified (quartz) 

 veins often exhibit a remarkable folded or corrugated structure 

 within the beds of slate that contain them. The corrugations, or 

 crenulations, usually occur at or near the apex of the anticline, and 

 run parallel with one another and in a direction approximately par- 

 allel with the axis of the fold." He believes (i) that the veins were 

 formed during the folding of the region; (2) that, due to differential 

 motion within the relatively weak or plastic slate containing veins 

 which were formed early in the folding process, the veins and inclos- 

 ing slate were corrugated; and (3) that such motion resulting in 

 corrugations took place mainly at the apexes of the folds. 



DIFFERENTIAL SQUEEZING ACCOMPANYING REGIONAL FOLDING 



Lateral pressure may result in the folding of certain weaker 

 strata while adjacent more resistant strata take up the thrust either 

 without so much folding or by being fractured instead of folded. 

 Intercalated beds of limestones are especially likely to yield in this 

 manner. Interesting effects of differential squeezing in the folded 

 Algonkian strata of the Marquette district of Michigan have been 

 described by Van Hise, Bayley, and Smyth^ who say: 



Along the contacts of the (Kona) dolomite beds and the quartz (ite) layers 

 accommodation was necessary, and in places a bed of limestone may be seen 

 bent into a series of anticlines and synclines, the overlying quartzite not being 

 similarly bent, but being compressed and brecciated, thus making a pseudo- 

 conglomerate When the series was folded the more plastic limestone 



yielded to the pressure, in both a major and a minor way, by folding, while the 

 brittle quartzite was fractured through and through, the movement of the 

 fragments over one another, and of the beds as a whole, being suflSicient to 

 truncate the minor waves of the marble. 



1 E. R. Faribault, Can. Geol. Surv., Guide Book No. i, Part i (1913), PP- 174-88. 



2 Van Hise, Bayley, and Smyth, U.S. Geol. Surv., Mon. 28 (1897), pp. 242-43. 



