6io WILLIAM J. MILLER 



zones. Still farther east the mixed rocks are nearly all straight- 

 banded. It is believed that, during the forcing in of the magma, 

 the whole mass of rock was notably plastic, and that local differential 

 movements within the mass, caused by unequal pressures of the 

 rising magma, resulted in the local corrugations. 



MAGMATIC FLOWAGE 



Finally, in our discussion of intraformational contorted rocks, 

 differential magmatic flowage should be mentioned as a cause. 

 Within certain areas of plu tonic igneous rocks which exhibit primary 

 foliation, there are not uncommonly local zones or bands in which 

 the gneissoid structure, accentuated by dark minerals, appears to 

 be irregular, wavy, or even contorted. The writer's experience in 

 the Adirondacks shows' such local, contorted, primary flow-struc- 

 tures to be very common there, especially in the great syenite- 

 granite series, and it is beHeved that they are essentially the result 

 of varying magmatic currents under differential pressure, principally 

 during a late stage of magma consoHdation. 



Lawson^ has noted similar structures within certain granites of 

 the Rainy Lake region of Ontario. He says: ''The hnes of streak- 

 ing are very often not straight, but are wavy or contorted, sometimes 

 intricately so, and are evidently due to slow movements in the 

 magma prior to final consolidation." 



' W.J. Miller, Jour. Geol., Vol. XXIV (1916), pp. 611-12. 

 2 A. C. Lawson, Can. Geol. Surv,, Mem. 40 (1913), p. 93. 



