38 NEW YORK STATE MUSEUM 



lated a great excess of orthoclase and strong affinities with the 

 syenites. There are no exposures of anorthosite in the North Creek 

 area, but the gabbros have come up through granite-porphyry, 

 granite, quartz-syenite, and Grenville gneisses. If now we imagine 

 a quartz-orthoclase Grenville gneiss caught up in a lime-rich, anor- 

 thosite magma and impregnated with the latter, a richly garnetiferous 

 rock, with enlarged proportions of bisilicates might easily result. 

 Even an aggregate not appreciably different from a garnetiferous 

 member of the syenite series is possible. An origin of this sort for 

 the basic syenitic masses which have been now several times encoun- 

 tered and which have been extremely difficult to classify, is deserving 

 of very serious consideration. 



The Garnet " reaction-rims " of the anorthosites. Since the 

 time of Professor Leeds's studies upon the anorthosites the presence 

 in them of rims of garnet surrounding the pyroxene and titaniferous 

 magnetite has been a matter of record and knowledge. In the sum- 

 mer of 1 914 the writer collected some exceptionally good material 

 from a large boulder on the Chapel Pond road from the Keene 

 valley to the valley of the Schroon river. Fortunately in the fall of 

 1 91 4, Max Roesler, who had had some years of experience with 

 the contact zones between intrusive rocks and limestones in Arizona, 

 was studying with the writer at Columbia University, and under- 

 took the investigation of the reaction-rims. Mr Roesler in the latter 

 half of the university year became instructor in the Sheffield Scien- 

 tific School at Yale University and completed his paper at the latter 

 institution, where he had the valuable advice and suggestions of 

 Professor Pirsson and the aid of Dr Walter F. Bradley in the chemi- 

 cal analysis. The results are here introduced as a contribution on 

 one feature of the anorthosites which is of much petrographic 

 interest. Coming after the recent studies of Prof. W. J. Miller on 

 similar developments in the gabbros of the North Creek quadrangle, 

 Mr Roesler's paper carries the subject a step further. For the con- 

 tribution the writer takes pleasure in expressing his indebtedness. 



