SOME PRE-CAMBRIAN LITERATURE OF NORTH AMERICA 471 



rocks, 42 per cent diabase, and 33 per cent by the Keewatin. The 

 Huronian had 53 productive veins, the Keewatin 6, and the diabase 

 7. Assuming that these areas have prospected equally well, the 

 chances of finding ore are about 9 times better on the Huronian 

 than on an equal area of Keewatin, and about one-twelfth as good 

 on the diabase as on an equal area of Huronian. 



Miller^ reports that the pre-Cambrian rocks exposed in the 

 district of Patricia, comprising over 146,400 square miles west of 

 James Bay, which has recently been added to the Province of 

 Ontario, include limestones similar to those of the Hastings and 

 Grenville districts, a small volume of Lower-Middle Huronian con- 

 glomerates, iron-bearing Animikie, and diabase intrusives, probably 

 Keweenawan. 



Miller and Knight^ state that they have found an unconformity 

 between the Grenville and the Hastings series of eastern Ontario, 

 the Hastings being younger. The Grenville, they maintain, has 

 been deposited on rocks similar to the Keewatin greenstones of Lake 

 Superior, and the Grenville, therefore, may be the time equivalent 

 of the Keewatin iron formations farther west. The Hastings series 

 they regard as Huronian. 



Moore^ describes the geology of the Sturgeon Lake goldfield in 

 191 1. It is located in latitude 50° north longitude, northwest of 

 Thunder Bay. The rocks are pre-Cambrian, largely igneous, 

 including granites, gneisses, aplites, quartz-porphyries, rhyolites, 

 hornblende-syenite, diorites, diabase, basalts, gabbros, and por- 

 phyrites and their metamorphic equivalents. There are small 

 patches of arkose, graywacke, and dolomite. The relations of the 

 igneous rocks to each other is partially known, but the age of the 

 sediments and the igneous rocks and their relations are still uncer- 

 tain. Free-milhng gold veins are found at contacts, and in cleavage 

 and fault planes and other openings. The gangue is principally 



' W. G. Miller, "District of Patricia," Ont. Bur. Mines, XXI, Pt. 2, pp. 200, 18 

 figs., 29 maps. 



^W. G. Miller and C. W. Knight, " Grenville-Hastings Unconformity," Abstract, 

 Geol. Soc. Am. Bull., XIX (1909), 539-40. 



3 E. S. Moore, "The Sturgeon Lake Gold Field," Onl. Bur. Mines, 20th Ann. Kept. 

 pp. 133-57, 17 figs. 



