28 NEW YORK STATE MUSEUM 



or more or less assimilated, the border facies of the anorthosite. 

 Detailed field evidence in support of this view is presented below. 



Gushing maintains that the chilled border is fatal to Bowen's 

 conception that molten overlying syenite may have been faulted 

 down against solid anorthosite so that it could have laterally 

 attacked the anorthosite, thus accounting for the intrusive features 

 including the syenite dikes. Much detailed field work by the writer 

 shows that the chilled border (Whiteface anorthosite) grades 

 directly into the typical anorthosite, and that there is no reason to 

 think that the syenite-granite series developed between the chilled 

 border and the typical Marcy anorthosite. Even if we assume, 

 what has not been found in the field, that some such syenite or 

 granite exists as a rock intermediate between the chilled border 

 and the typical anorthosite, it is most unreasonable to suppose that 

 the chilled border would, in some places, grade first into the syenite 

 or granite and then into the Marcy anorthosite. Either one of 

 these might be the case, but not both. 



Bo wen suggests that the syenite-granite may have developed 

 between the chilled border and the Marcy anorthosite, and then 

 have been reintruded through the chilled border. But how can we 

 possibly imagine such a vast bulk of syenite-granite to have been 

 so largely reintruded that not any of it has been discovered in its 

 supposedly original position? Also how can we imagine the rein- 

 trusion of such a tremendous volume of syenite-granite through 

 the chilled border facies, leaving this latter as a definite fringe 

 about, and grading into, the Marcy anorthosite for so many miles ? 



Dikes of syenite and granite in anorthosite. Some years ago, 

 in his report on the Geology of the Long Lake Quadrangle? Gush- 

 ing showed that several narrow well-defined dikes of syenite there 

 cut the typical Marcy anorthosite, one of these dikes being several 

 miles within the border of the great anorthosite body. He also 

 states that one of the small outlying masses of anorthosite is 

 " definitely cut by syenite which sends dikes into it." 



As a result of the surveys of both the Lake Placid and Schroon 

 Lake quadrangles by the writer, various excellent examples of 

 dikes and broad tongues of syenite and granite cutting anorthosite 

 have come to light. A number of fine examples of such dikes are 

 described in the report on the Geology of the Lake Placid Quad- 

 rangle. 



*N. Y. State Mus. Bui. 115, p. 480-84. 1907. 



