INTRAFORMATIONAL CORRUGATED ROCKS 607 



hydration of anhydrite, as can be observed in many places. Since 

 the gj^sum beds occur in a very shallow syncline, the highly 

 crenulated intercalated layers cannot have been caused by regional 

 folding. The cause was, no doubt, the force exerted within the 

 whole mass as a result of the great expansion during the trans- 

 formation of anhydrite to gypsum. Differential stresses and 

 strains set up locally in the whole mass caused locaKzation of the 

 corrugations (Fig. 9). 



Fig. 9. — A specimen of gypsum from Hillsborough, New Brtmswick, showing 

 highly folded layers between less folded layers. 



PRESSURE OF INTRUDING MAGMAS 



Among the pre-Cambrian rocks of the Adirondack Mountains, 

 New York, the writer has observed excellent examples of intra- 

 formational corrugations which are believed to have been direct 

 effects of the pressure of magmatic intrusions. He has presented 

 evidence^ to support the view that the very ancient Grenville 

 stratified series has never been subjected to severe regional folding 

 throughout most or all of the Adirondacks. During the intrusion 

 of the tremendous volumes of syenite-granite magma, the Grenville 

 series was, however, badly cut to pieces so that many masses, 

 both small and great, were tilted about in the rising magma and in 

 many places subjected to notable differential pressure. The Hme- 

 stones, especially where they are near contacts with the syenite- 



^ W. J. Miller, Jour. Geol., Vol. XXIV (1916), pp. 595-96. 



