﻿GEOLOGY OF THOUSAND ISLANDS REGION 35 



gneiss " with its characteristic yellowish tinge on weathered sur- 

 faces, is but sparingly present in our area here. In the district 

 east of Redwood it occurs somewhat, as it does also to the north- 

 ward of Theresa. It is a quartzose gneiss, usually containing the 

 mineral " sillimanite " and holding pyrite in quantity, the easy de- 

 composition of which is chiefly accountable for the weakness and 

 the color stain of the rock. 



There are reddish, acid gneisses which, so far as composition 

 goes might be either original granites, or shaly sandstones. There 

 are black and white gneisses, which are feldspar-pyroxene-quartz 

 gneisses. There are very granular, dark reddish, weak, microper- 

 thitic feldspar-hornblende gneisses; gray, f eld-spar-hornblende 

 gneisses, holding much pyrite and titanite; there are leaf -quartz 

 gneisses, the quartz in coarse spindles or lenses, and with little 

 other than feldspar in addition; evenly granular, white, spotted 

 gneisses which are microperthite-quartz-hornblende rocks; garneti- 

 ferous, quartz-biotite gneisses, with but little feldspar and a lot of 

 pyrite; quartz-feldspar-phlogopite gneisses with graphite; gneisses 

 which somewhat suggest metamorphosed volcanic tuffs, though in 

 no case has it been possible to demonstrate such an origin for them. 

 Many of the rocks contain calcite, which at times has resulted 

 from alteration and at times suggests itself as an original constit- 

 uent. Graphite is a frequent mineral in many of the schists. 



Nowhere in the district has a rock been found which at all sug- 

 gests the greenstones of the Keewatin formation. 



Belts of badly altered rock, considerably impregnated with iron, 

 so as to constitute lean iron ore, occur within the Grenville schist 

 belts, striking with the belt and apparently behaving like an in- 

 tegral part of the series. Fragments of one such belt are found 

 in the granite of the Alexandria bathylith near Cranberry creek, 

 and a prominent belt occurs east of Redwood, especially along the 

 north side of Millsite lake. The rock is exceedingly weak, earthy 

 looking, either red, or yellow brown in color, and has a consider- 

 able local use for road metal. It is so thoroughly altered that it is 

 almost impossible to get any clear notion of its original character 

 being simply a mass of clayey, alteration products, with consider- 

 able calcite, and the whole impregnated with hydrated iron oxid, 

 chiefly the red oxid. There are fresher streaks and bunches here 

 and there which appear to be granite gneiss. None of the so 

 called " serpentine " rock, which is generally associated with the 

 similar, but richer, belt of iron ore which runs through Antwerp 



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