INTRAFORMATIONAL CORRUGATED ROCKS 595 



Under conditions of differential movement the wide belt of predomi- 

 nant phyllite yielded by development of corrugations, while the 

 thin bands of phyllite between much quartzite on either side yielded 

 by development of fracture cleavage. 



In the Marquette syncHnorium of Michigan intraformational 

 corrugations are shown on large scales in the slate formations which 

 lie between quartzite formations. 



During the summer of 192 1 the writer was impressed by the 

 fine exhibitions of intraformational contorted strata of Proterozoic 



Fig. 4. — Ground-plan sketch of intraformational corrugated phyUite and quartzite 

 near Ogunquit, Maine. The black lenses are quartz. Contorted zone about 9 feet 

 wide. 



age on both small and large scales in Glacier National Park. In 

 the waU of the great Swiftcurrent cirque, only a few rods from the 

 trail, the strata are notably folded and even crumpled through a 

 thickness of 30 to 40 feet, and for a distance of a few hundred feet, 

 while on all sides the strata are undisturbed except for the moderate 

 regional tilting. The folding rocks are not sharply separated from 

 the others. On the grand scale the strata are very irregularly con- 

 torted through a thickness of hundreds of feet in the face of the 

 mountain between Gunsight Lake and Gunsight Pass with non- 

 contorted strata above, and also at the same general horizon on 

 either side. These contorted beds have quite certainly resulted 

 from local differential movements within the great body of Protero- 

 zoic strata either during the development of the synclinal structure 



