INTRODUCTION. 



The Sudbury region is especially known for its nickel 

 mines, the most important in the world ; but the geologist 

 finds an almost equal interest in its eruptive rocks, which 

 include a remarkable basin-shaped laccolithic sill more than 

 a mile thick and covering 400 square miles of territory, and 

 its unusually complete set of pre-Cambrian formations, prob- 

 ably not surpassed by any other area of equal size in 

 America. The region displays also striated rock surfaces 

 and boulder clay, due to Pleistocene glaciers and shore and 

 deeper water deposits of ancient Lake Algonquin. 



The scenery of the region is mostly of the " rocky lake " 

 character, but this is diversified with considerable stretches 

 of fertile farm lands. In many parts the original forest has 

 been destroyed by the lumberman and by fire, leaving the 

 rock hills bare, so that the geological structures are admir- 

 ably exposed ; and in a few places sulphur fumes from roast 

 beds and smelters have destroyed all vegetation, allowing 

 rain to carve the drift materials and expose the glacier 

 smoothed rock surfaces beneath. 



The most striking physiographic features of the region 

 are connected with the great basin-shaped sheet of the nickel 

 eruptive. This consists of an easily-weathered outer side of 

 norite blending into a resistant inner side of a granitic char- 

 acter, whch has metamorphosed and hardened the rocks 

 above; so that after passing the irregular Archaean surface 

 which surrounds the basin, there is everywhere a depression 

 or trough, sometimes occupied by lakes, representing the 

 basic portion of the eruptive, followed after a mile or two 

 by rugged hills, made up of the acid portion and the meta- 

 morphosed sediments above. 



After crossing this belt of rough hills the interior spreads 

 out as a low plain covered with old lake deposits, often 

 level as a prairie. From the farms of the interior one sees 

 the rim of the basin rising on all sides as ridges or hills 

 sometimes reaching 500 feet above the sheltered plain. The 

 basin is drained by Vermilion river and its tributaries, 

 which descend as fine cataracts and falls when their course 

 leads over the acid edge, or meander with a gentle current 



11 



