GEOLOGY OF THE LONG LAKE QUADRANGLE 475 



Long ponds, the rock at first is the granitic phase of the syenite, 

 cut by dikes of fine grained red granite. This is shortly replaced 

 by a variable rock which seems clearly a basic phase of the ordinary 

 syenite, also cut by the red granite. At the extreme top is the 

 anorthosite, extending about 300 yards in a northeast-southwest 

 direction. The rock is quite typical, is medium grained, and labra- 

 dorite feldspar constitutes 95% of it, magnetite, augite, chalcopy- 

 rite and apatite being the other minerals. Not only is the passage 

 from the syenite to the anorthosite abrupt, but in addition the latter 

 is all cut up by dikes of the former, both large and small. It is also 

 cut by dikes of the same red granite as that found cutting the 

 previous rocks. 



On its northwest side the anorthosite is cut out by a reddish 

 syenite whose relations to the main syenite are not absolutely 

 certain, though if it be not identical it is a closely related rock. 

 Red granite again occurs cutting both the other rocks. The anor- 

 thosite is badly cut up by them and has been much altered in ap- 

 pearance, likely by the heat and gases given off by the invading 

 molten rock. The feldspar has been mostly converted to saussu- 

 rite, producing a dull, white rock. 



This exposure, though small, is of much interest in that it clearly 

 shows anorthosite cut by syenite, which is therefore younger, and 

 granite cutting both the others and therefore youngest of all, the 

 anorthosite being entirely surrounded by the other rocks, and there- 

 fore an inclosure in them. A plausible explanation of its position, 

 so remote from the main mass, and its inclosed situation in the later 

 eruptives may be made by the following assumptions: that the 

 anorthosite batholite originally extended to the locality, or else 

 sent a large offshoot to it ; that the later syenite invaded it and cut 

 it out from beneath, sending out at the same time the big tongue of 

 syenite which cuts out the anorthosite clear to the Raquette river ; 

 that the anorthosite inclusions indicate that the present surface is 

 not far beneath the original upper surface of the syenite; that 

 Grenville rocks originally overlay the whole, and have since been 

 removed by erosion; and that later trough faulting dropped the 

 block of Grenville that lies between, so that it has been less worn 

 awa}^, the syenite and anorthosite beneath still retaining a Gren- 

 ville cover, though it has disappeared elsewhere. 



The second anorthosite outlier is near the county line (Franklin- 

 Hamilton) I J miles from the west edge of the quadrangle. On the 



