PHYSIOGRAPHIC HISTORY OF NORTHEASTERN ONTARIO 207 



at least as far as Duluth. How far eastward they extended is not 

 known, nor, owing to the cover of Palaeozoic sediments, how far 

 south. 



Between Keweenawan and Ordovician time these late Pre- 

 cambrian (Killarnean) mountains were worn down to a condition 

 probably not greatly different from that of the Adirondacks today, 

 and certainly greater rehef than the Lacloche Mountains of today, 

 for these latter have since endured additional erosion from Palae- 

 ozoic time onward. A few peaks of the Killarnean Mountains 

 now project through the Palaeozoics on Manitouhn Island; and 

 bore-holes that have been made near by in the search for oil indi- 

 cate a submountainous local rehef of more than 800 feet in the floor 

 upon which the Ordovician formations were laid. 



Let us next consider the period of time that elapsed from the 

 commencement of deposition of the Dore sedimentary series until 

 the Timiskaming series and Sudbury series were completed. The 

 Dore series is almost certainly of continental origin. It is thought 

 to have been deposited under conditions Hke those which governed 

 the deposition of the silts and gravels in the interior plateau of 

 British Columbia. The Keewatin volcanics are beheved by some 

 geologists to be of submarine origin, owing to the abundance among 

 them of ellipsoical greenstone ; but the writer can find no evidence 

 to support this view. It appears, rather, that they were deposited 

 on land and in small bodies of water. Recent studies of the 

 Timiskaming series by Mr. H. C. Cooke' indicate a continental 

 origin for this series also. Judging by the extremely variable 

 thickness of the sediments throughout this group, their coarse 

 texture, and apparently local deposition, the region may have been 

 one of considerable topographic relief during the entire time. 



Except in the southern portion of northeastern Ontario, these 

 formations are extraordinarily folded, schistified and faulted, and 

 invaded by granite bathohths of huge size. In fact, they are 

 represented now only by irregular patches which were down-folded 

 low enough to escape erosion. If intense regional disturbance and 

 batholithic invasion indicate mountain-building, it must be con- 



' "Kenogami Lake and Larder Lake Areas," Geol. Surv., Can., Memoir in course 

 of publication. 



