308 



NEW YORK STATE MUSEUM 



date; the uncertainty connected with the matter arises from the 

 fact that in no case has it so far been possible to trace these dikes 

 to any connection with the near-by larger masses, of which they 

 are thought to represent offshoots, so that the correlation between 

 the two depends merely on rock similarity. At the one or two 

 exposed contacts it seems quite certain that the anorthosite is 

 the older rock, but here again there is some question as to the 

 actual identity of the rock which cuts it. 



At two localities near the anorthosite boundary, border rocks 

 haye been discovered which, instead of exhibiting the ordinary 

 change to anorthosite gabbro, disclose a gradation toward syenite. 

 Such haye only been noted in localities where the anorthosite is 

 bordered by a syenite which is thought to be younger, and the 

 rock represents a transition stage between the two, though much 

 closer to anorthosite than to syenite. The precise significance of 

 these rocks is not known, the field exposures not being sufficient 

 to giye any idea of the relationships to the two rocks, and, since 

 the presence of an intermediate rock of this sort can be accounted 

 for in several ways, and gives no evidence as to the relative age 

 of the other rocks, speculation on the subject is of no value, in 

 the lack of corroborative field evidence. 



Anorthosite outliers. In the northern Adirondacks there are 

 two considerable anorthosite outliers in Clinton county and two 

 very small ones in Franklin county. Xot unlikely other small 

 ones will be discovered when the region is mapped in detail, work 

 of this sort on the Long Lake sheet of the new topographic maps 

 during the past season having first brought to light the two 

 Franklin county outliers mentioned above. Kemp has mapped 

 several on the south in Essex and Warren counties. 



The two Clinton county outliers are those at Keeseville and 

 Rand hill. The former is not strictly an outlier but rather a 

 tonguelike offshoot from the main mass, the connection being 

 bared by erosion. As in all the outliers, the rock here exhibits 

 the characters of the border portions of the main mass rather than 

 of its center, in other words is anorthosite gabbro. not so coarse 

 grained as, but more gneissoid than the usual rock, with from 



