BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 Vol. 1, pp. 175-194 March 20, 1890 



THE INTERNAL RELATIONS AND TAXONOMY OF THE 

 ARCHEAN OF CENTRAL CANADA. 



BY ANDREW C. LAWSON, PH. D. 



(Ri'Uil before tJte Society December 28, 1889.) 



CONTENTS. 



Page. 



Primary Separation of the Archean into two Divisions 175 



The Upper Division 176 



Nomenclature 176 



Petrographical Description 177 



Original Characters and Metamorphism 180 



delations between the two Divisions 181 



The General Relations 181 



Irruptive Contact on Lake of the Woods 182 



Irruptive Contact in Rainy Lake Region 183 



Significance of Relationship 185 



Principles of Classification ... 186 



Principles applicable to the Upper Division 186 



Principles applicable to the Lower Division 18G 



Different Generations of Laurentian Rocks 187 



Other Conditions considered 187 



Similar Observations elsewhere 188 



Geognostical Equivalents of the Archean 190 



The Argument from Analogy 193 



Primary Separation of the Archean into two Divisions. 



Throughout North America, geologists have long recognized in the great 

 fundamental complex of rocks, known generally to-day as the Archean, a 

 natural division into two well-characterized portions, related to each other 

 in space as upper and lower. The lower division is commonly known as 

 the Laurentian, and consists for the most part of an assemblage of rocks of 

 the character of granites, syenites, diorites, and gabbros in mineralogical 

 composition, but more or less foliated or gneissic. Involved with these in a 

 way not hitherto understood there are also, in sorr? regions, portions of 



(175) 



