1 SN> A. C. LAWSON — RELATIONS OF THE ARCHEAN OF CANADA. 



crustal magma mighl be irrupted within the overlying crustal rocks without 

 the intense folding of the latter. Here we should expect to find a less pro- 

 nounced alteration, due only to the proximity of the magma, and an absence 

 of those phases of metamorphism which accompany the rock shearing, crush- 

 ing, and stretching due to dynamic agencies, [n the common case, where 

 the upper crustal rocks are folded, varying phenomena would also be ob- 

 served according as the folding took place before the fusion which produced 

 the magma immediately beneath the crust or while the latter was Boating 

 upon the magma. 



There are also more complicated cases which are doubtless common. 

 These are due to the superimposed action of crust-crumpling, rock-shearing, 

 strata-squeezing forces subsequent to the establishment of the Archean con- 

 ditions in their primal simplicity. These are possibilities which must be 

 borne in mind in attempts to apply the theory lure advanced to the Archean 

 in other regions. It is easily conceivable that had the country northwest of 

 Lake Superior been subjected to extensive deformation in post-Archean 

 times, the evidence whereby the irruptive character of the Laurentian has 



been demonstrated might have been entirely obscured, and the true relation- 

 ship might have remained unsuspected, as appears to have been the case in 

 better known regions. 



Similar Observations elsewhere. 



In various parts of the world observations have been recorded which show 

 that the phenomena arising from the irruption of a local or general sub- 

 crusta] magma through an overlying crust, and the consequent development 

 of a complex of gneissic igneous rocks and metamorphic strata, are not 

 peculiar to the region studied by the writer. 



MacFarlane* long ago described and figured good evidence of the irrup- 

 tive character of the Laurentian of the northeast shore of Lake Superior; 

 but, iii accordance with the views of the extreme plutonic school, he regarded 



the whole complex of intrU8ive and intruded mcks as the first crust of the 



earth, and the angular fragments of hornblende schist a- earlier separations 

 from the same magma a- thai which crystallized into the Laurentian granite 

 or Byenite-gni iss. 



Mr. Prank Adam-, who ha- been for some years past engaged in a atudj 



of the Laurentian of the Province of Quebec, north of the St. Lawrence, 



— 



The unexpected fact wa lined thai the so-called massive and Btra titled 



ilu- rock [anortbosite ; hithert< led :e upper Laurentian and meta- 



3., Vol. Ill, 1867, p. 177. 



