ADIRONDACK MAGNETIC IRON ORES I3I 



north and east of Harris ville, recognizable gabbro outcrops 

 have been found. These rocks, it may be noted, are compara- 

 tively rare, in contrast with their wide distribution elsewhere in the 

 Adirondacks. 



A prominent member of the gneiss series is a coarse reddish 

 hornblende rock which has the composition of granite. It is abun- 

 dant in the region east of Harris ville, particularly between Benson 

 Mines and Cranberry lake and the section northward. Its affinities 

 are with the igneous rocks, as indicated by field evidence in places, 

 though further investigation is needed to prove that the gneiss is 

 of uniform character and derivation. 



Certain representatives of the gneisses are undoubted meta- 

 morphosed sediments, yet contain no included bands of limestone. 

 Their sedimentary origin is traced by their mineralogical and 

 textural peculiarities. They have a variable composition,' light 

 colored quartzose varieties alternating across the strike with dark 

 varieties in which there is a considerable proportion of hornblende, 

 mica or pyroxene. Garnet is a frequent constituent and pyrite is 

 seldom wanting. Sillimanite also appears, but rarely in crystals 

 sufficiently large to be distinguished without the aid of the micro- 

 scope. The constituents have a granular habit, without the definite 

 arrangement or texture which obtains in igneous rocks. These 

 gneisses are to be classed as members of the Gren ville series. They 

 are very much like the hornblende and mica gneisses that occur 

 over large areas in the eastern Adirondacks and which have been 

 assigned to the base of the Grenville. 



Description of mines 



Benson mines. The deposits are in the town of Clifton, on the 

 north side of Little river. Benson Mines is a hamlet and a railroad 

 station, 43 miles east of Carthage. The valley lies at an elevation 

 of about 1600 feet, while the limiting ridges are somewhat more 

 than 2000 feet. 



In his report on the Second District, 1 Emmons mentions the 

 occurrence of magnetite bodies on the Oswegatchie river near the 

 crossing of the former highway known as the Albany road. From 

 the accompanying description it is evident that the present Benson 

 mines are referred to; and the stream now known as Little river 

 was probably designated on the old maps as the Oswegatchie of 

 which it is a tributary. Emmons states that a considerable quan- 



Survey of the Second Geological District. 1842. p. 347. 



