GEOLOGY OF THE SCHROON LAKE QUADRANGLE 97 



of graphite, many of which range from i to 5 miUimeters across. 

 This extra rich layer was the one principally worked. A band 

 of crystalline limestone a few feet thick, containing graphite and 

 green pyroxene, lies in contact with the graphite schist. The strike 

 of the rock is N 50° W and the dip S 60°. Some small workings 

 are at the surface, but the main operation was running a shaft said 

 to be 75 feet deep and now filled with water. 



Graphite flakes commonly occur scattered through the crystalline 

 limestone of the Grenville areas around Minerva and Olmsted- 

 ville, but not in such form or quantity as to be commercial at 

 present. 



Garnet 



On the hill one-third of a mile southwest of Calahan pond, there 

 are two places close together where red garnet was mined to some 

 extent a good many years ago. In the smaller mine opening, which 

 lies just west of the map boundary, the garnet, in irregular to 

 rounded highly fractured masses up to several inches in diameter, 

 is associated with Grenville coarse crystalline limestone and con- 

 siderable green pyroxene in crude crystals up to an inch in length. 

 This Grenville is twisted into gneissoid granite, the relationship 

 being very clear. Some much smaller inclusions of pyroxene and 

 garnet rock are sharply defined in the granite. The larger opening, 

 whose location is indicated on the map, is 50 feet long and 30 feet 

 wide. It shows similar rocks except that no granite actually appears 

 in the mine opening. Granite does, however, outcrop only a few 

 rods away. It is probable that these garnets developed during the 

 process of metamorphism along and close to the contact between 

 the Grenville strata and the granite. 



Garnets occur in various other rocks of the quadrangle, being 

 especially abundant in certain of the Grenville hornblende-garnet 

 gneisses, and in certain facies of the anorthosite and syenite-granite 

 series, but in all these the garnets are generally too small and scat- 

 tering to be of commercial value. 



Iron Ore 



Minerva mine. This small mine is situated 2^ miles due north 

 of Minerva village or three-fifths of a mile southeast of Sherman 

 pond and at an altitude of 1900 feet (see map). The Burden Iron 

 Company conducted the last mining operations in 1881 and sent 

 the ore to Troy. 



