2o6 W. H. COLLINS 



shown that the northeastern part of the continent, released from 

 its load of ice, has readjusted itself, since the Glacial period, by 

 gentle rising and tilting movements. There are no violently dis- 

 turbed formations among these. There can be no doubt, then, that 

 from Ordovician time until now northeastern Ontario has experi- 

 enced only gentle oscillations in level and shallow marine submer- 

 gence. 



Let us take next the section of time from the beginning of the 

 Bruce period until the end of the Keweenawan. This time is 

 represented by a blanket of sediments aggregating over 30,000 feet 

 in thickness, in the southern part of the region of northeastern 

 Ontario, but thinned out to nothing by erosion, toward the north. 

 The Bruce series is in part a land formation, and was for the remain- 

 ing part apparently laid down at the edge of a continent ; the Co- 

 balt and Keweenawan series are both continental. In the northern 

 part, these formations (represented by the Cobalt series) lie almost 

 flat, or in open folds. Consequently it can be said with assurance 

 that from the time of their deposition this northern part of the 

 region has experienced no movements but those of rise and fall and 

 mild compressional folding. Tracing these sediments southward, 

 however, they become progressively more closely folded. South 

 of a line drawn eastward and westward through Wanapitei Lake, 

 the folds are tight and have a definite eastwest, axial course. Small 

 masses of granite, intrusive in all these formations, appear at 

 Cartier, at Sudbury, and at other points and, finally, in a Une 

 running northeasterly from Killarney, the Bruce series and later 

 Precambrian sediments are abruptly truncated by a granite batho- 

 Hth of undetermined extent. How far southward this condition 

 extends cannot be ascertained, because, from Lake Huron south- 

 ward, the Precambrian formations are covered by the horizontal 

 Palaeozoics. 



It is abundantly clear that — if the associated phenomena of 

 close regional folding and bathoHthic invasion indicate mountain- 

 building — in late Precambrian time the southern part of the region 

 shown on this map was compressed to form a system of mountains. 

 These mountains occupied only the southern part of northeastern 

 Ontario. They extended west along the south side of Lake Superior 



