86 PROCEEDINGS OF THE CANADIAN INSTITUTE. 



and volcanic representatives of the gabbro group. Their relations may be shown 

 in tabular form as follows: 



Plutonic Gabbro. 



i 



Dyke Gabbro porphyrite. 



O 



^ Ivnlranir (Diabase. 



rt volcanic jAugite porphyrite. 



O V 



Whether the rock here placed under the dyke division be considered to belong 

 there or under the volcanic division we have an interesting series which includes 

 the characteristic pre-Potsdam basic rocks of the two districts. Representatives of 

 other sub-divisions of the gabbro dyke rocks, viz.: gabbro aplite (or beer- 

 bachite) and gabbro lamprophyre (or odinite) have not as yet been found in the 

 districts under consideration. 



