6o8 



WILLIAM J. MILLER 



granite, much more commonly exhibit local corrugations or crump- 

 Hngs than the other more rigid strata. Where a mass of the Gren- 

 viUe strata contains zones of well-bedded Hmestone intercalated 

 between more rigid strata, and the whole has been subjected to 

 differential pressure by the invading magma, the limestone layers 

 have not uncommonly become contorted by differential movement 

 within the mass while the adjacent beds above and below have been 

 deformed little or not at all. In Figure lo, which well illustrates 

 such a phenomenon in northern New York, the contorted beds of 



Fig. io. — Crumpled beds of impure, thin-bedded, crystalline limestone between 

 beds of only slightly disturbed garnetiferous gneiss north of Hermon, St. Lawrence 

 County, New York. 



very plastic impure limestone lie between heavy beds of rigid 

 garnetiferous gneiss. This contorted limestone and its associated 

 gneiss form part of a long narrow body of Grenville strata which 

 was included in, and subjected to differential pressure by, a large 

 body of granite magma, causing the more plastic limestone beds to 

 crumple. 



Spurr,^ in his discussion of the Silver Peak region of Nevada, 

 publishes a fine picture of intraformational contorted strata which 

 occur on Mineral Ridge. In this region large volumes of granite 

 magma invaded and cut to pieces Paleozoic strata made up of 



' J. E. Spurr, U.S. Geol. Surv. Prof. Paper 55 (1906), p. 108 and PI. 21, 



