Cobalt Series, 



The period of erosion that succeeded the intrusion of the 

 Lorrain granite gave rise to the conglomerate and other 

 rocks known as the Cobalt series. Good exposures of these 

 rocks are to be seen at Cobalt and along the railway to the 

 south and to the north. At Porcupine only small exposures 

 are found. The Ramsay Lake conglomerate of Sudbury 

 appears to be of the same age. 



In the Sudbury area there is also a series of sediments 

 which has been mapped as of Animikie age. The age 

 relation of this series to the Cobalt series and to the Ramsay 

 Lake conglomerate is not definitely known. 



Nipissing Diabase and Sudbury Norite. 



Succeeding the deposition of the Cobalt series came the 

 intrusion of the quartz-diabase which gave rise to the silver 

 deposits of Cobalt. This intrusive is known as the Nipis- 

 sing diabase. As stated above, the Sudbury norite, with 

 which are genetically connected the nickel-copper deposits, 

 is similar in chemical composition and appears to be of the 

 same age. 



Paleozoic Rocks. 



To the north and east of Cobalt, limestone, with basal 

 conglomerate and sandstone, of Silurian (Niagara) age, 

 occurs as outliers on the pre-Cambrian. 



With the exception of deposits of glacial and recent age, 

 no rocks younger than the pre-Cambrian are found in the 

 vicinity of Sudbury or Porcupine. 



W. G. M. 



Toronto, June, 1913. 



