10 NEW YORK STATE MUSEUM 



logic map as such. Occurrences of this kind will be described 

 later. 



One of the strongest proofs of the sedimentary origin of the 

 Grenville is the presence of limestone beds in the formation. 

 Such limestones have been described by Smyth^ in the Diana- 

 Pitcairn area some 30 miles northward and also at the Ful- 

 ton chain -of lakes some 25 miles eastward. A little has been 

 found by Mr D. H. Newland in the Little Falls district and 

 2lso on Moose river a few miles east of the Port Ley den quad- 

 rangle. The latter occurrence is the closest to the Port Leyden 

 quadrangle so far known. The writer has found no actual lime- 

 stone on either the Remsen or the Port Leyden sheet although 

 certain gneisses usually associated with the limestone are pres- 

 ent. The statement may be repeated that, whereas Grenville 

 limestone is common along the northwestern Adirondacks, it is 

 only sparingly represented along the southwestern border. 



The fact that commonly the Grenville rocks here and else- 

 where are in alternating layers which stand out in sharp con- 

 trast because of marked differences in composition and color 

 leads to the belief that these bands are due to differences in 

 original sedimentation. At times the gneiss is composed of 

 almost pure quartz and could scarcely be of igneous origin. 



Graphite is a form of crystallized carbon and of organic origin. 

 Its presence as flakes in certain of the Grenville gneisses, in- 

 cluding some within this quadrangle, affords a strong argument 

 in favor of the sedimentary origin of those gneisses. Garnet is 

 frequently present, often in great abundance, and it is rather 

 more common in metamorphosed sediments. 



Of the three areas above mentioned, each has certain dis- 

 tinctive features and hence they will be separately described. 

 Thus in the Kosterville area the rocks are mostly quartz-silli- 

 manite gneisses in thin layers and weathering to a rusty brown. 

 They are not sharply separated from the neighboring rocks and 

 some feldspar-garnet gneisses appear near the northern border 

 of the area and along the river below Shuetown. The dip of 

 the foliation is northward while the strike is about n. 60° e. 

 which is the same as for the surrounding rocks. The specimens 

 here described were taken from the fine exposures just below 

 the bridge across Moose river. Microscopic study shows one 



1 Crystalline Rocks of the Western Adirondack Region. N. Y. State 

 Mus. 51st An. Rep't. 1897. 2:469-97. 



