SOME PRE-CAMBRIAN LITERATURE OF NORTH AMERICA 469 



are named. The richest veins are in the Huronian. Hore supports 

 the views that the silver-bearing solutions came from the Kewee- 

 nawan diabase, that the Keewatin greenstone played an important 

 role in their deposition, and that the coarse Huronian sediments 

 afforded abundant openings for their reception. 



Hore' states that the diabase of the Cobalt district occurs in 

 dikes and sills intrusive into Keewatin schists, and Huronian sedi- 

 ments. The minerals of the diabase are pyroxenes, plagioclase, 

 quartz ilmenite, biotite, and olivine. Olivine seems to be confined 

 to small masses of diabase showing no differentiation. Aplitic 

 micropegmatitic intergrowths of sodic feldspar and quartz, some- 

 times with calcite, occur in the thick sills. Some of the micro- 

 pegmatite is clearly a differentiate of the diabase in situ, occurring 

 in spots and stringers grading into the diabase. Some of it is a later 

 differentiate, fiUing fissures sometimes with selvage borders. 



A minor fissure filling in the diabase consists of quartz, with 

 chlorite and amphibole. Galena, pyrite, and chalcopyrite are 

 frequently present. Calcite sometimes fills interstices between 

 well-formed crystals of calcite. 



King^ describes a lens-shaped deposit of low phosphorus, non- 

 titaniferous magnetite ore, which occurs at the contact between 

 Grenville limestone and Laurentian granite at the Wilbur mine, in 

 Lanark County of eastern Ontario. 



Knight^ presents diagrams showing faults in the Cobalt district. 

 The largest known fault has a displacement of over two hundred 

 feet. It is of the reversed type and strikes parallel to the longer 

 axis of Cobalt Lake. 



Kerr'' presents a petrographic description of the Port Caldwell 

 syenite area on the north shore of Lake Superior about 125 miles 

 east of Port Arthur. The principal rock of the region is nepheline 



'Reginald E. Hore, "Diabase of the Cobalt District, Ontario," Jour. Geol., 

 XVIII, No. 3 (1910), 27of. 



2 Shirley King, "The Wilbur Iron Mine," Jour. Can. Min. InsL, XII (1909), 

 582-91. 



3 C. W. Knight, "Recent Underground Development Work at Cobalt," Jour. Can. 

 Min. Inst., XV, No. 18 (1912), pp. 21-23, ^ pl- 



'' H. L. Kerr, "Nepheline Syenites of Port Caldwell," Onl. Bur. Mines, icjlh Ann ^ 

 RepL, Pt. I, pp. 194-232, 20 figs., I map. 



