4 8 4 



NEW YORK STATE MUSEUM 



northern and western Adirondack^. The anorthosite, syenite and 

 granite are all characterized by sudden and very great variations in 

 the distribution of the ferro-magnesian constituents. These con- 

 stituents may be gathered together, giving the rock locally the ap- 

 pearance of a gabbro, or they may be wanting altogether, giving in 

 the case of the anorthosite a pure plagioclase rock, in the case of 

 the syenite a plagioclase, orthoclase and microperthite rock, and in 

 the case of the granite an orthoclase, quartz, microperthite rock. 

 The basic varieties are the confusing ones, for with increasing ferro- 

 magnesian Constituents the three types approach each other very 

 closely. Later than all three is the typical gabbro. All are plutonie 

 and younger than the sediments. 



Granite. Granitic rocks form a considerable area in the south- 

 west, including Pharaoh mountain and several unnamed peaks of 

 some importance. The rock, usually pink in color, is a hornblende 

 granite, but sometimes contains considerable quantities of biotite. 

 It is frequently gneissic, the granite gneiss sometimes being hard to 

 distinguish from the syenite gneiss and the gabbro-gneiss. The 

 igneous gneisses may readily be separated from the sedimentary 

 ones by their massive character and by their uniform appearance 

 over wide areas. 



That this granite is later than and intruded into the limestone 

 series is indicated by numerous pegmatite dikes and bosses. In 

 passing from Mount Pharaoh to Mount Treadway one traverses first 

 coarse granite dikes, then pegmatites, and finally to the east of 

 Treadway, quartz veins. This is strongly suggestive of the natural 

 and normal relations which so often occur around intrusives. 



Syenite. Rocks of this type are proving to be one of the com- 

 monest of Adirondack intrusives. The type was first described by 

 Dr Smyth, and has since been found in many localities, proving to 

 be an extensive component of the gneissic areas. 1 



The occurrence in the Paradox Lake quadrangle is in all respects 

 similar to those already described. 



1 Smyth, C. H. jr. Geol. Soc. Amer. Bui. 6:271-274; N. Y. State Geol. i;th 

 An. Rept 1899. p.471-486. 



Gushing, H. P. Geol. Soc. Amer. Bui. 10:177-192; N. Y. State Geol. 18th 

 An. Rept 1899. .P.105-T09. 



