New York State Museum 



PKE-OAMBRIAN OUTLIER AT LITTLE FALLS, HERKI- 

 MER CO. 



Little Falls is a locality possessing much geologic interest 

 from several points of view, and has been visited by many geolo- 

 gists. But little attention has been paid however to the nature 

 of the crystalline rocks here exposed. 



Vanuxem mentions the rock at this locality as " gneiss," 

 though noting a tendency to assume a porphyritic character.^ 

 Hall at a much later date calls the rock labradorite (anorthoslte 

 of recent reports) evidently regarding it as the same as the Essex 

 county rock. 2 



Kemp (probably following Hall) refers to the reported presence 

 of the " labradorite rocks " at Little Falls, but quotes no author- 

 ity for the reference.^ 



Prosser and Oumings, in reporting to the state geologist in 

 1895, make a brief reference to the pre-Cambrian at Little Falls.* 

 They refer to the rocks as " gneiss " and a^ ^^ garnetiferous 

 gneiss ", and report it as having a thickness of 203 feet above the 

 river. Their work was specially concerned with the Lower Silur- 

 ian formations, and the reference to the pre-Cambrian is merely 

 incidental. Since the rock is igneous, the measured thick- 

 ness has not the significance that would attach to it were it 

 sedimentary. The part of their section from which garnetiferous 

 gneiss was reported was not seen by the writer. This mineral is 

 rare or wholly lacking in the writer's section. 



Beyond these four statements the writer has met in literature 

 no reference to the character of these pre-Cambrian rocks. The 

 rock is however not anorthoslte (labradorite rock) but syenite. 

 Prof. Smyth seems to have been the first to recognize this, and 

 stated to the writer that such was its character during a con- 

 ference just preceding the visit to the locality. From specimens 



^ Geol. N. Y. 3d geol- district, p. 19-20. 



^ N. Y. state geol. 5th an. rep't 1885, p. 8-10; reprinted in 14tli an. rep't 

 1894. p. 54-56. 



^ N. Y. state geol. 17th an. rep't 1897, p. 505. 



* Prosser and Cumings. N. Y. state geol. 15th an. rep't 1895. p. 633. 



