480 NEW YORK STATE MUSEUM 



boundary between the two rocks might furnish proof of its verity. 

 This was in fact one of the principal reasons for the selection of 

 this quadrangle for detailed study. The hope was fulfilled, the 

 evidence being as decisive as could be desired. 



About Raquette falls, on both sides of the river, anorthosite 

 and syenite are found in mixed distribution. All exposures are 

 in the woods, in no case was any contact observed, and it is only 

 by the relative abundance and distribution of the two rocks as 

 brought out by the mapping that it is inferred that east of 

 the river the syenite is present as small bosses or large dikes, 

 cutting the anorthosite, while west of it the anorthosite has been 

 largely cut out and mostly occurs as inclosures in the syenite. 



The evidence given by the first anorthosite outlier in Litch- 

 field park has been already presented. The anorthosite is defi- 

 nitely cut by syenite which sends dikes into it. The syenite is of 

 the basic variety in part, and in part is reddish syenite; the whole 

 is surrounded by a zone of mixed rocks, granitic syenite and 

 granite which, though believed to be mostly a differentiation 

 phase of the syenite, lies between it and the normal syenite farther 

 north, preventing the definite tracing of one rock into the other. 



It is along the northern edge of the quadrangle, where the 

 land has been cruelly lumbered of late years, where the great 

 fire of May 1904 made a clean sweep of what was left, and where 

 much of the land has since been cleared, that the decisive evi- 

 dence was obtained. Even as far east as Upper Saranac lake 

 occasional dikes are found cutting the anorthosite. These are 

 narrow, the dike rock is fine grained and peculiar and of two 

 main types. One is a hard, ringing, light colored, feldspathic 

 rock, with frequent small garnets, but with other dark minerals 

 present but sparingly. The other is a dark, heavy, gabbroic- 

 looking rock, with abundant garnet. From its appearance in the 

 field it might be either a gabbro or a basic syenite. Now while 

 these rocks suggest syenite in appearance they differ much from 

 the main body of the rock, which shows no similar phases. Yet 

 it is obvious that the physical conditions under which they cooled 

 differ so much from those under which the larger masses solidi- 

 fied, that a considerable difference in appearance and character 

 is normal,, rather than abnormal. And the study of thin sections 

 led to the confident belief that they were really dike offshoots 

 from the main mass prior to the discovery of decisive field evidence. 



