46 NEW YORK STATE MUSEUM 



granitic rocks. The texture gives no clue to its original nature, 

 being completely granulated in most specimens. The quartz 

 particles seem to be an earlier crystallization than the feldspar, 

 contrary to the usual order of igneous rocks. 



Sedimentary crystallines. The principal members of the sedi- 

 mentary or Grenville series are limestone, hornblende gneiss and 

 mica schist. Dr Ogilvie has recorded the presence of quart zite 

 and sillimanite gneiss in the upper part of the series, but they have 

 no representation within the limits of the district. The sedimen- 

 tary derivatives are closely associated in their field relations. 



The limestone forms bands and larger belts that are followed by 

 the stream courses. It is thoroughly crystalline and frequently 

 contains such minerals as graphite, pyroxene, amphibole and 

 phlogopite and other silicates that have originated from the 

 alteration of the limestone and its impurities by metamorphic 

 agencies. 



The hornblendic and micaceous gneisses and schists though 

 completely changed from their original condition show indubitable 

 evidences of their sedimentary derivation. They are as a rule 

 very quart zose, with a proportionately small amount of feldspar 

 and varying quantities of hornblende and mica. They are con- 

 spicuously banded; beds of light and dark varieties alternate 

 across the strike, their junctions being sharp like the planes sepa- 

 rating different sedimentary beds. Garnet, pyrite and occasionally 

 graphite occur as accessory minerals. 



Intrusive rocks. Of the recognizable intrusives found in the 

 Hammondville district, the anorthosite and gabbro are uniform 

 in their geology and mineral character with the general types 

 which constitute the central Adirondacks. They grade into each 

 other by imperceptible stages and have no doubt originated from 

 a common magma. The syenite may also belong to the same 

 intrusive series, representing a more acidic development. It is 

 made up of microperthite, hornblende and a green augite, but in 

 some phases contains labradorite feldspar as well and shows a 

 gradation toward the gabbro. These rocks are all later than the 

 sedimentary formations which are invaded by them, though the 

 relations can be determined infrequently by contact effects owing 

 to the regional metamorphism that has taken place subsequent to 

 their intrusion. 



The granite found on Knob mountain and in small areas within 

 the gneisses is a coarse reddish variety. It contains microcline as 

 the principal feldspar, with some orthoclase and quartz, horn- 



