86 NEW YORK STATE MUSEUM 



quadrangle next west^ where they constitute the lofty peaks in this 

 center of elevation. 



In their structural relations they can only be described as a huge 

 batholith or irregular mass of vast size. Whether there were suc- 

 cessive intrusions of the typical anorthosites or not, no evidence 

 has been found. There is visible mineralogical variation in the 

 greater or less amounts of the pyroxenic component, and in the 

 development of biotite in the exposures east of Elizabethtown, but 

 this does not necessarily imply separate intrusive masses. 



Where the borders of the anorthosites follow a stream valley 

 their outline is quite certainly conditioned by faulting, and we 

 might infer enough displacement to produce decided discordance, 

 but this relationship is rare, and the fault lines usually pay slight 

 attention to formational borders. 



Pronounced eruptive contacts have been observed in several in- 

 stances. In the cascades of Slide brook and Coughlin brook which 

 enter the upper Boquet river from the west are very instructive ex- 

 posures. Another that is more accessible is in the Branch just 

 below the junction of the Windsor hotel road and the main road 

 between Elizabethtown and Keene. From the bridge at the junc- 

 tion for 200 yards or so down stream to and beyond the mill the 

 brook flows over the contact of the anorthosite and the dioritic 

 gabbro while a small basaltic dike passes from one rock to the 

 other, with very interesting illustrations of the effects of cooling. 

 The relations are shown in figure 4, which is based on a pacing 

 survey. 



Aside from these intrusive contacts it is soon learned that the 

 border of the anorthosite mass is almost always more basic than 

 the central portions. Harris hill, a marked elevation in western 

 Moriah, is an exception, probably because it is a fault block, but 

 elsewhere these relations almost always hold. 



There are two small outliers of anorthosite, neither a perfectly 

 typical case of the rock, but both referable to this series much more 

 closely than to any other. One is a coarsely crystalline garnetiferous 

 variety at the western end of Crowfoot pond, where it is well 

 shown in the talus. The other is -farther west along the old road 

 which passes Crowfoot pond. Since both occur in the midst of areas 

 regarded as belonging to the syenite series, and since the latter 

 are believed to be later than the anorthosites, the two small areas 

 must be surviving islands or huge inclusions. 



Areal distribution of the Split Rock Falls type. The main area 

 of this rock lies along the upper Boquet river above New Russia. 



