BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 Vol. 5, pp. 481-488 April 18, 1894 



MICA DEPOSITS IN THE LAURENTIAN OF THE OTTAWA 



DISTRICT 



BY R. W. ELLS 



(Presented before the Society December 28, 1893) 

 CONTENTS 



Page 



Introductory 481 



Rock Groups of the Region 482 



Metamorphosed Sedimentaries 482 



Intrusives 482 



Former Errors in Identification 482 



Minerals 483 



Rock Relations determined by Minerals 483 



Occurrence of Apatite and Mica 484 



Mica- Apatite Horizon 485 



Mode of Occurrence of the Micas 486 



Differences observable in the Mica-Apatite Deposits 487 



Mica Localities 488 



Introductory. 



Recent investigations upon the Laurentian rocks which have such an 

 enormous development in Canada have shown that the views formerly 

 held as to their structure and origin must to a large extent be modified. 

 This change of views applies with equal force to the theories at one time 

 put forth to account for the presence of certain economic minerals for 

 which these rocks have long been celebrated. 



Rock Groups of the Region. 



Metamorphosed Sedimentaries. — From the composition, structural ar- 

 rangement and general relations of large portions of that great rock 

 system, it appears that certain beds found therein present many of the 

 features peculiar to deposits originally sedimentary, and that these beds 



LXVII— Bull. Geol. Soc. Am., Vol. 5, 1893. (481) 



