172 Canadian Record of Science. 



well developed, while the supposed lower gneiss, on account 

 of its great development about the head waters of the Ot- 

 tawa Kiver was known afterwards by the name of " Ottawa 

 gneiss." As a result of later investigations, in other parts 

 of Canada, Vennor came to the conclusion that the higher 

 division rested unconformably upon the lower gneiss. 

 Whether therefore wo have two distinct and unconformable 

 series or not is a point which is not as yet conclusively 

 determined. The facts hitherto collected, however, would 

 rather indicate that the two are distinct. In the present 

 essay these two names (Grenville series and Ottawa 

 gneiss) will be employed to designate these two de- 

 velopments of the Laurentain respectively, and it 

 may be here remarked that whether they be con- 

 formable or * unconformable, considered from the eco- 

 nomical standpoint, there is a very marked difference 

 between them. The Grenville division with its crystalline 

 limestones, quartzite, &c, carries apatite, graphite, iron 

 ores, mica and in general all the important mineral deposits 

 of the Laurentian, while the Ottawa gneiss, as far as we at 

 present know, carries but little in the way ot valuable 

 minerals. 



In the Grenville series we find also the earliest traces of 

 life on our planet, since the undoubted occurrence of larger 

 as well as smaller limestone beds which so frequently al- 

 ternate with the gneiss of this series can only be explained 

 by organic agencies. The presence of a considerable ad- 

 mixture of graphite, which in many of these limestones 

 occurs in a finely dissiminated condition, and is also found 

 in many cases in the associated gneisses, is a further im- 

 portant testimony in the same direction. Many of these 

 limestones resemble precisely some of younger age where 

 these have been metamorphosed by contact with eruptive 

 rocks. The carbon of the limestone crystallizes as graphite 

 in these cases, and the clayey substances, take the form of 

 small scales of mica or grains of other minerals. Veins of 

 graphite appear likewise, though sparingly, in these Lau- 

 rentian limestones and correspond to the veins and strings 



