r32 NEW YORK STATE MUSEUM 



Section between Saranac and Lake Clear, N. Y. C. & H. R. R. R. 



Between these two points the railroad closely foUow^s the edge 

 of the anorthosite mass. At first the G^renville rocks adjoin, 

 but for most of the distance gneisses with a little augite 

 syenite. It is possible that we are dealing with a fault contact, 

 though by no means certain. 



Just at Saranac the rocks are gneisises which are referred to 

 the Grenyille series. But the first rock cut (804), at the south 

 end of Colby pond, shows anorthosite. Here, while portions of 

 the rock have coarse and numerous labradorite crystals, the 

 major part is thoroughly granular and, in its considerable con- 

 tent of dark silicates, recalls the hyperite gabbros. At least 20^ 

 of the rock is constituted of minerals other than feldspar, the 

 minerals present being apatite, magnetite, garnet, augite, 

 bronzite, hornblende, plagioclase feldspar and quartz. While 

 one feldspar section shows equal extinctions of 20° from the 

 albite twinning plane on both sides, the majority shows 10° or 

 less, so that most of the feldspar is not more basic than andesin. 

 There is only a little quartz, associated with garnet in the corro- 

 sion rims which have so often been described from these rocks* 

 This rock is not necessarily more basic than the usual anortho- 

 site, but would seem to have about the same silica with dimin- 

 ished alumina and lime and increased iron, magnesia and alkali 

 percentage. Very similar rock shows in a ridge by the road 

 some 300 yards east of the Ampersand hotel. 



A second and long one, running to the point where the railway 

 skirts the west extremity of the pond (805) is 40 rods beyond this 

 cut. In this the rock is at first fine grained and looks precisely 

 like the last, but it becomes progressively coarser and more 

 porphyritic, becoming quite typical anorthosite at the farther 

 end. Midway of the cut is a dike of apparent gabbro some 30 

 feet wide (80oA). In the coarse rock at the farther end of the 

 cut the large labradorites show flow structure, having a parallel 

 alinement. Here is also an apparent dike of grahite, though it 

 may be merely a huge inclusion, its great difference in width on 

 the opposite sides of the cut favoring this view. 



