13 



through the old lake deposits of the interior. The spread- 

 ing out of the sheet of molten rock and its settling into a 

 synclinal basin have given a regularity to the topographic 

 forms not found in other pre-Cambrian regions, and rivers 

 and lakes and farms and railway routes are all adjusted to 

 the ancient rock structures. 



Sudbury itself, the capital town of the region, lies some 

 miles southeast of the edge of the basin and rests upon older 

 rocks with a less orderly arrangement. They include near 

 Wanup and Quartz on the Canadian Pacific and Canadian 

 Northern railways, characteristc rocks of the Grenville 

 Series, whose position with reference to the classification 

 adopted by the International Committee is somewhat uncer- 

 tain ; and also a great series of other sediments older than 

 the Laurentian, which have recently been proved to lie 

 below the Huronian, and which have been named provision- 

 ally the Sudbury series. 



The most recent classification of the pre-Cambrian in the 

 Sudbury region is as follows : 



Post Keweenawan( ?) — Dikes of diabase and granite. 



Keweenawan ( ?) — Xickel-bearing eruptive sheet. 



Huronian— Upper Huronian (Animikie), conglomerate, 

 tuff, slate and sandstone. 

 " — (Middle Huronian wanting.) 



— Lower Huronian, basal conglomerate. 



Laurentian — Granite and gneiss eruptive through older 



rocks. 

 Sudbury Series — Copper Cliff arkose, McKim graywacke, 



and Ramsay Lake quartzite. 



Keewatin — Iron Formation, greenstones and green schists. 



Grenville Series — Quartzite, sillimanite schists and gneisses 

 and crystalline limestone. 



Whether the Keewatin and the Grenville series are of the 

 same age or not is uncertain, since the two groups of rocks 

 do not occur together. 



As no fossil-bearing rocks have been found the position 

 in time of the later eruptives is somewhat doubtful, as indi- 

 cated in the table. 



