434 Canadian Record of Science. 



ment : in Canada, in Norway, in Kussia, and in Egypt. 

 They are found in enormous masses in the first three 

 countries, and their extent is not yet known in the last 

 mentioned. To these occurrences others will probably 

 be added as the Archaean of other parts of the world is 

 carefully studied. 



VII. SUMMARY OF RESULTS. 



1. The " Upper Laurentian," or the " Anorthosite group'" 

 of Sir William Logan, does not exist as an independent 

 geological formation. 



2. The anorthosite, which was considered to be its 

 principal constituent, is an intrusive rock of the gabbro 

 family, and is characterized by a great preponderance of 

 plagioclase, of which mineral the rock is, in fact, often 

 entirely composed. 



3. The rock is in places perfectly massive, but it 

 generally exhibits the irregular structure which is so 

 often observed in the gabbros, and which is brought about 

 by a variation in the size of the grain or of the propor- 

 tion of the ingredients from place to place. In addition 

 to this original structure, the rock almost always shows a 

 peculiar cataclastic structure which is especially well 

 developed in the foliated varieties. This differs from the 

 structures characteristic of dynamic metamorphism in the 

 great mountainous districts of the world, being produced 

 by movements in the rock mass while this was still deeply 

 buried in the crust of the earth, and probably very hot — 

 perhaps near its melting point. 



4. In all the cases of supposed unconformable super- 

 position of the anorthosite upon the Laurentian gneisses, 

 which have been carefully investigated, the unconforma- 

 bility is found to be due to intrusion. 



5. The rock occurs in a series of isolated areas, some ef 

 which are of enormous extent. 



6. These areas are without exception at or near the 



