256 J. F. KEMP — ROCKS OF THE EASTERN ADIRONDACKS. 



At a number of localities in Ticonderoga township there is a gneissoid 

 rock, intimately associated with the limestones and schists, containing 

 plagioclase and often scapolite and a curious lavender-colored pyroxene 

 with a pink tinge. Its optical properties are not essentially different 

 from normal pyroxene, but the color is peculiar. This gneiss is abundant 

 just north of Rogers rock, where it is intimately associated with limestone. 

 The same pyroxene is found in silicate bunches in the limestone along 

 with garnet and scapolite. 



The abundance of augite in the gneissoid rocks is very striking and of 

 the bisilicates it is the most common and widespread. 



It should be further stated that the limestones and schists are pene- 

 trated by gabbro intrusions of great size, and that, as shown in figures 

 3 and 5, intrusive contacts are not lacking. On the lake-shore north of 

 Port Henry they are wonderfully displayed. There is no marked de- 

 velopment of contact-minerals in these exposures, but the bunches of 

 silicates are large and appear to be fragments of the gabbro which 

 became involved in the limestone in the great dynamic stresses to which 

 the latter was subjected. At distances from these gabbros dikes much 

 metamorphosed have penetrated the limestones and have even been 

 drawn apart so that the limestone has been forced in between the sun- 

 dered edges in a way closely simulating igneous intrusions. The quarry 

 near the Pilfershire mine affords a fine illustration of this. The Foote 

 quarry near Port Henry shows a great sheet at its upper crest. In ad- 

 dition to these sheared and metamorphosed dikes, there are frequent 

 exposures of other narrow, unchanged diabasic ones which have come 

 through at a late period in the history of the rocks. 



THE KEENE TYPE LOCALITY. 



General Description. — An area of the limestone series is met about a 

 mile southwest of Keene Center, in the heart of the Adirondacks. It 

 extends, as nearly as one can tell, some three-quarters of a mile along the 

 outcrop, but is of uncertain width, apparently not over 1,000 feet. It ap- 

 pears to be the final termination southward of the belt, which comes up 

 the valley of the Ausable river from the north and is found in detached 

 outcrops in this direction in Jay township. The tj^pical anorthosites of 

 the Adirondacks surround it on all sides, but to the east, in the valley 

 of the river, granite also occurs. 



The area is of some exceptional interest because the limestone con- 

 tains a deposit of iron ore which has proved quite productive in the 

 past. The limestone is thickly charged with pyroxene and graphite, 

 but it is not notably serpentinized. 



