PRE-CAMBRIAN ROCKS IN ONTARIO 581 



The temporary section of stratigraphy organized with H. S. Williams 

 as Chairman and J. F. Kemp as Secretary. The following six papers 

 were read : 



PRE-CAMBRIAN ROCKS IN THE VICINITY OF LAKE TEMISKAMING, ONTARIO 



BY WII/LET G. MILLER 



[Abstract] 



Two areas of pre-Cambrian rocks in northwestern Ontario, those of the " Original 

 Huronian" area on lake Huron and of the Rainy River district, have been some- 

 what closely studied, and the reports on them have become almost classic. Lake 

 Temiskaming, which is on the eastern boundary of the province, lies over 200 

 miles east of the former area. Although numerous descriptions have been pub- 

 lished of the crystalline rocks of the region lying between these two localities, little 

 success has been achieved in subdividing ahd classifying them. A. E. Barlow's 

 work of a year ago showed that there are two series in the vicinity of lake Temagami, 

 an older complex igneous group and a j^ounger fragmental group, together with 

 later intrusions. 



During a part of the past summer the writer has been engaged in mapping an area 

 of about 15 miles square which lies at the northwest corner of lake Temiskaming, 

 25 miles north of Temagami. In this area he has discovered two unconformable 

 fragmental series among the pre-Cambrian rocks. (1) The oldest group of rocks 

 here is similar to the older of the two groups at Temagami. It consists of a complex 

 assemblage of igneous rocks which may be broadly divided into three varieties, 

 although others are present. The oldest of the varieties can now be called a green- 

 stone. It is cut by quartz-porphyry. The two have been subjected to folding and 

 are cut by granite. (2) After the granite eruption, erosion has taken place, giving 

 rise to conglomerate and finer-grained, slate-like varieties. (3) There has been a 

 second period of erosion, and deposited on the surfaces of the two older series there 

 is a group or series of arkose and quartzite. (4) Each of these three series or 

 groups is cut by diabases and gabbros of pre-Paleozoic age. 



The oldest of these series of lake Temiskaming, the greenstone and quartz-por- 

 phyry with intruded granite, may, for the present at least, be correlated with the 

 Thessalon greenstone, with associated granite, of the "Original Huronian," and 

 with a part of the Keewatin of the Rainy River district; while the second series, 

 that of the conglomerates and slate-like rocks, corresponds, in this area, to the 

 conglomerate of the Lower Huronian of lake Huron. The arkose series of Temis- 

 kaming, which is unconformable to the conglomerate and slate, may here be con- 

 sidered to represent Logan's Upper Huronian of lake Huron. More detailed work 

 may, however, show that there are still other unconformities in the Temiskaming 

 area. 



The second group or series, the conglomerate and slate, is of economic interest 

 on account of the occurrence in it of ore deposits which, so far as is known, are 

 unique on this continent. The ores are found in fissures, which, in dip, approach 

 the vertical, cutting through the usually slightly inclined conglomerates and slates. 

 Ore is being shipped from four properties. The chief ores are native silver, smal- 

 tite, andniccolite. Associated with these are native bismuth, erythrite,annabergite, 

 chloanthite, cobaltite, mispickel, millerite, argentite, dyscrasite, pyrargyrite r 



