ROGERS, GEOLOGY OF THE CORTLANDT SERIES 57 



separating two bands, the individual grains seem to interlock across the 

 line. The only remaining hypothesis, therefore, is that of the intrusion 

 of a molten mass already heterogeneous. 



Harker 44 appears to favor the view that the structure is due to the 

 approximately simultaneous intrusion of two different magmas, which 

 would give rise to an interpenetration of the two. This would account 

 for the banded structure, which always shows evidence of flowage and is 

 seldom straight and clear cut. The assumption would be then, of course, 

 that the mass would soon begin to cool and harden while resting quietly, 

 as otherwise the two magmas might combine to form a third and homo- 

 geneous one. Harker's alternative view is that the mass was intruded as 

 a unit, already heterogeneous, the two different magmas having been 

 partly mixed before intrusion. Whichever be the correct theory, it is evi- 

 dent that in the Cortlandt Series the simple norite magma was very small 

 in comparison with the more complex norite magmas, since the former is 

 always as included bands in the others, while these latter cover con- 

 siderable areas. 



Kelations of the Types, with Analyses 



From the above description of the more salient characters of the Cort- 

 landt Series, it appears that we have in it a fairly complete and very 

 intricate complex, one susceptible and worth}' of the most detailed study. 

 In some places — e. g., Montrose and Stony Points — the complexity of the 

 mass is bewildering, while again we may have several miles of a fairly 

 uniform rock. At times, as shown in the original gneissoid structure, the 

 contacts are sharp and clear, although never showing contact metamor- 

 phism on each other, while again numerous cases have been noticed of- 

 one rock grading into another. Thus, for example, the biotite norite area 

 at Lenf s Cove grades into the biotite augite norite to the south by a 

 perfect series of steps; similarly the augite norite at Montrose. Diorite 

 becomes hornblendite, and pyroxenite becomes chrysolitic, by imper- 

 ceptible gradations. Moreover, the different larger groups are similarly 

 connected; the diorite just southeast of Pleasantside grades into the ad- 

 joining hornblende norite, and norite passes into olivine pyroxenite by 

 way of olivine norite. An infinite number of species might be differen- 

 tiated within this small area of twenty-five miles ; in this paper only the 

 unavoidable ones have been mentioned. The accompanying diagram 

 (fig. 2), greatly modified from Williams, is designed to show in a rough 

 way the relations of the species. The lines connecting the circles indi- 

 cate the direction in which gradation has been most frequently observed. 



" Natural History of Igneous Rocks, pp. 13S and 341. New York, 1909. 



