ANAL YTICAL ABSTRA CTS. Ill 



mentary geological formation, but it is discordantly upon the gneiss of the 

 Laurentian by intrusion. Its intrusive character is shown by the following 

 facts : it is a plagioclase gabbro ; it cuts across the Laurentian schists ; it holds 

 as inclusions blocks of gneiss ; about its masses forming girdles are many 

 characteristic contact belts. The areas of anorthosite are isolated, and lie 

 along the border of the Archean continent of that time exactly as the volcanoes 

 of to-day are along the continental borders. In the great interior area of 

 Laurentian no anorthosite has been found. The formation is all pre-Cambrian, 

 as shown by the fact that it lies unconformably below the Cambrian. Also 

 before the Cambrian was deposited it received its metamorphism, and was 

 deeply eroded. Its relations to the Huronian have not been determined, but 

 it probably does not belong to the Huronian period, but rather to the closing 

 part of the Laurentian. 



The several regions of anorthosite are described separately, that of Morin 

 and Saguenay being most fully considered. The Morin area is surrounded 

 by the Grenville series. In the Grenville series are interlaminated limestones, 

 bands of which can be traced many miles. Within the limestone are 

 frequently thin layers of the gneiss. The limestone is less resistant and more 

 plastic than the gneiss. As a result of folding, the bands of gneiss have been 

 broken up, producing irregular banded blocks, which are isolated in the 

 limestone in such a manner as to give rise to extraordinary pseudo-con- 

 glomerates. 



The Saguenay region is of great size, 5,800 square miles. It is surrounded 

 on all sides by the orthoclase-gneiss, or Ottawa gneiss. The anorthosite of 

 this district is more basic than that of the Morin district, the plagioclase 

 frequently being labradorite or bytownite. That it is an intrusive is shown by 

 the same facts as in the Morin area. 



Comments. — The time of pre-Cambrian life must have been so vast that it 

 is not safe to assume that the rocks of the original Laurentian bear the 

 remains of the first life of the planet. Indeed, it seems probable that the 

 earliest life left in the rocks no permanent evidence of existence. Further, 

 before it can be assumed that the Ottawa Laurentian bears the oldest 

 remains of life, it must be shown that these rocks are older than any other 

 series bearing life remains. 



Adams describes the typical Laurentian areas of Canada.^ The basement 

 rock here found is the Fundamental Gneiss. It is uniformly reddish or grayish 

 orthoclase-bearing gneissoid granite, poor in mica, and bisilicates. The foliation 

 is often due to movement in a plastic condition. Dark bands of amphibolite 



' On the Typical Laurentian Areas of Canada, by Frank D. Adams. Journal of 

 Geol., Vol. I., No. 4, pp. 325-340. 



