IS6 A. c. r.AWSON — RELATIONS OF THE ARCHEAN OF CANADA. 



they could nol have been deposited upon a magma. There must have been 

 a firm crusf presenting a floor upon which they were laid down. That floor, 

 together with portions of the system of rocks which lay piled upon it, has 

 disappeared. That it has sunk down to a zone of fusion and become ab- 

 sorbed by liquefaction in a Bub-crustal magma, which later crystallized nut 

 as the Lauren tian, is the only explanation that is open to us. It follows 

 also thai the Laurentian rocks arc younger than those of the Ontarian sys- 

 tem, as has been before indicated. 



Prin< rPLES of ( Ilassifk V.TION. 



The bearing of the tacts and conclusions recorded above upon the tax- 

 onomy of the Archean is apparent. The argument establishes this cardinal 

 principle in the classification of that great complex of rocks, viz., thai its 

 primary subdivision depends upon a distinction of cosmical importance be- 

 tween an older assemblage of altered normal surface-formed strata and a 

 younger assemblage of rocks resulting from the crystallization of a sub- 

 crustal magma. 



Principles applicable to the Upper Division. — To. the upper or Ontarian 

 system the ordinary stratigraphical methods of classification are applicable. 

 The svstem separates stratigraphically into two great groups. The lower 

 and older, consisting of strata t'vov from volcanic admixtures, so far as has 

 been observed, is the Coutchiching. It resembles in its lithological charac- 

 ters and in it- position the Montalban of Hitchcock. The upper group, 

 consisting of rocks which are dominantly volcanic in composition, is the 

 Keewatin. It rests upon the Coutchiching in probable unconformity, the 

 beginning of the period in which these rocks were deposited being signalized 

 l>v the advent of a widespread and continued volcanic activity. This group 

 falls into line with the Green Mountain series in the position assigned to it 

 by Hitchcock. Other groups may quite possibly be discovered which will 

 swell the volume of the Ontarian system. 



Principles applicable to the Lower Division. — In the Laurentian the ordi- 

 nals si ratigraphical principles of classification do not apply, since there are 

 no strata properly so called; and we must seek for a principle appropriate 

 to an assemblage of rock- essentially different in their development and 

 mode of occurrence from all those of the Btral igraphical column. The Lau- 

 rentian is not homogeneous throughout its surface distribution. It is com- 

 posed ofdifferenl members or masses, which, while they present wonderfully 

 con-taut general characters within themselves, are distincl from one another 

 lithologically. A Btudy of the relationship between the masses thus differen- 

 tiated in Bpace leads us to the chief moment of all geological classification, 

 namely, their differentiation in time ; and we have to consider the possibility 



