326 THE JOURNAL OF GEOLOGY. 



ince of Quebec, was carried out by Logan and his assistants in 

 the early years of the Canadian Geological Survey. An excel- 

 lent resume of the results of these studies is given in the 

 "Geology of Canada," published in 1863, which contains not 

 only a good description of the general petrographical character 

 and arrangement of the rocks which make up the area, but is 

 accompanied by an atlas containing two maps illustrating this 

 description, one showing the general distribution of the Lauren- 

 tian in the eastern part of the Dominion, and the other its strati- 

 graphical relations in the smaller area above referred to. 



As a result of these studies, Logan announced his belief that 

 the Laurentian System consisted of two great unconformable 

 series of sedimentary rocks, to which he gave the names Upper 

 and Lower Laurentian. The latter he considered to be divisible 

 into a lower and an upper portion, which sub-divisions he 

 regarded as probably conformable to one another. In the course 

 of time these several series came to be known as the Anorthosite 

 or Norian Series, the Grenville Series and the Fundamental or 

 Ottawa Gneiss. Logan's views may then be represented as 

 follows : 



Anorthosite or Norian Series, Upper Laurentian. 



Grenville Series, Upper portion | Lower 



Fundamental or Ottawa Gneiss, Lower portion j Laurentian. 



Subsequently, in the southeastern corner of the Province of 

 Ontario, in the district lying to the north of the eastern end of 

 Lake Ontario, another series of rocks was discovered — the so- 

 called Hastings Series. Logan supposed this to come in above 

 the Grenville Series, while Vennor, who subsequently examined 

 the district, believed it to be equivalent to the lower part of the 

 Grenville Series already mentioned. 



When these investigations were carried out, the microscope had 

 not as yet been seriously employed in petrographical work. The 

 precise composition of many of the rocks making up the several 

 series was not recognized, the effects produced by great dynamic 

 action were not duly considered, and the foliation possessed in a 

 high degree by some and to a certain extent by almost all these 



