no THE JOURNAL OF GEOLOGY. 



The succession in the district, as determined in ascending order, is (i) 

 reddish grey gneiss without distinct signs of bedding or stratification, but with 

 a foliated structure ; (2) reddish orthoclase-gneiss interstratified with horn- 

 blendic, quartzose, and garnetiferous gneiss and beds of quartzite, the whole 

 showing a well stratified arrangement of beds ; (3) grayish and rusty gneiss 

 passing gradually upward into the calcareous portion of the system, between 

 the gneiss and the limestone there being interstratifications of the two ; and 

 (4) schistose, sericitic, chloritic, and micaceous schists of the Hastings series. 

 This division overlies the crystalline limestone, and is believed to represent 

 the lower member of the Huronian system. This arrangement of the Laur- 

 entian accords very closely with that in New Brunswick, as given by Bayley 

 and Mathew. Unconformable upon the Laurentian of Ontario is the Pale- 

 ozoic. 



Adams ' describes the anorthosite of Canada, and gives its relations to the 

 surrounding rocks. The great mass of the Archean of Canada is composed of 

 an orthoclase-gneiss, which is in many places laminated, but is in large part 

 little laminated, and probably of eruptive origin. Much of the laminated 

 gneiss is probably sedimentary. In certain regions the laminated gneiss is 

 interlaminated with crystalline limestones, quartzite, amphibolite, etc. This 

 series is a higher part of the Laurentian, and was called by Logan the Gren- 

 ville series ; while the lower gneiss, which does not bear any of this rock, was 

 called the Ottawa gneiss. The limestone, graphite, etc., are evidences of the 

 existence of life during the deposition of the Grenville series, and this was the 

 earliest life of the planet. 



All of the minerals of economic importance occur in the Grenville series. 

 The relations of the Grenville series to the Ottawa series have not been 

 certainly determined, but it is probable that the Grenville series lies discord- 

 antly upon the old gneiss, the upper series being sediments originally like 

 those that are deposited to-day. 



The anorthosite group, or Upper Laurentian of Logan, is an eruptive rock 

 belonging to the gabbros. It is characterized by a predominance of plagio- 

 clase, which frequently is the only mineral of the rock. The rock is hard and 

 originally was completely massive. This original structure has been modified 

 so as to take on an extraordinary cataclastic structure, which has also given the 

 rock a schistose character. This is not ordinary dynamic metamorphism, but 

 is caused by a movement of the rock mass while it was deeply buried and 

 near its melting point. 



The anorthosite, although so regarded by Logan, is not a distinct sedi- 



'Norian oder Ober-Laurentian von Canada, Adams, F. D. Inaugural-Dissertation 

 zur Erlangung der Doctorwurde der Universitat zu Heidelburg. 1893. 



