128 G. S. Rogers — Original Gneissoid Structure 



the white streak is merely a finer and therefore simpler facies, 

 containing only small amounts of biotite and augite. In one 

 place it shows an included patch of the coarser rock. Fig. 2 

 shows the same relations on a smaller scale, but in better 



Fig. 1. 



Fig. 2. 



Figs. 1, 2. Original gneissoid structure in the Cortlandt Series. 



development, so that the rock might easily be mistaken for a 

 real metamorphic gneiss. A number of other equally good 

 instances might be shown, for the structure is quite common ; 

 but these suffice to show its general aspect. It may be added 

 that none of the rocks of this series exhibit any great amount 



