S86 



WILLET G. MILLER AND CYRIL W. KNIGHT 



In conformity with the views of the time, Logan and his asso- 

 ciates considered the Laurentian to be made up essentially of 

 metamorphosed sedimentary material. With the passing of the 

 years, the Laurentian came to be looked upon as separable into 



Fig. I. — Geological sketch map of Ontario 



three groups: (i) Lower Laurentian or Ottawa series, consisting 

 essentially of granite gneiss; (2) Middle Laurentian or Grenville 

 series, consisting of crystalline limestone and other rocks; and 

 (3) Upper Laurentian or Norian. From the Laurentian groups 

 was first taken the Upper Laurentian, which was proved to be not 

 of sedimentary origin but an intrusive.^ Afterward the Grenville 

 ^ Neues Jahrb., Beilage Band 8, 1893, pp. 419-98. 



