734 A TREATISE ON METAMORPH1SM. 



Cases of claimed fusion of vastly greater magnitude than that at 

 Pigeon Point are described by Lawson, Barlow, and other members of the 

 Canadian survey. Lawson a has held that the great batholithic masses of 

 granite and gneiss, some of them many kilometers in diameter, in the 

 region of Rainy Lake and Lake of the Woods, northwest of Lake Supe- 

 rior, have been produced by the fusion of the sedimentary and volcanic 

 series, which he has called Keewatin and Coutchiching. He has called 

 this a case of subcrustal fusion. Similar statements have been made by 

 Barlow in reference to the batholiths of granite in the Original Huronian 

 district; 6 and the same thing has been said with reference to the granite and 

 gneiss of the Original Laurentian district. However, no adequate evidence 

 has been offered to support any of these conclusions. Composite chemical 

 analyses have not been made of the Keewatin and Coutchiching rocks and 

 the granites and gneisses supposed to be formed by their fusion, in order 

 to compare their compositions and thus to determine whether the granites 

 could possibly have been derived from the Keewatin and Coutchiching- 

 rocks by subcrustal fusion. All of the phenomena along the contacts of 

 the granitic rocks and the Keewatin and Coutchiching are such as may be 

 found at various parts of the world where batholiths of igneous rock have 

 intruded other rocks. Many frag'ments of the intruded rocks are included in 

 the intrusive. At many places there is a border belt in which the two are 

 intermingled in the most confused way, and, furthermore, in the intruded 

 rocks pegmatization has occurred adjacent to the batholith. The phenom- 

 ena might possibly lead one to infer the derivation of the intrusive rocks 

 from the intruded rocks by the fusion of the latter, and subsequent action 

 as an intrusion of the magma thus formed, but I do not so interpret them. 



I have gone over the Rainy Lake and Lake of the Woods region in 

 the field, and have visited and closely studied the specific localities described 

 by Lawson as giving evidence of subcrustal fusion. At every one of these 

 localities the phenomena are precisely those which generally occur where 

 great intrusive batholiths penetrate other rocks. For instance, at the Nar- 

 rows of Kaiarskons Lake, which is cited by Lawson c as one of the best 



« Lawson, A. C, The internal relations and taxonomy of the Archean of central Canada: Bull. 

 Geol. Soc. America, vol. 4, 1890, pp. 185-186. 



b Barlow, A. E., Relations of the Laurentian and Huronian rocks north of Lake Huron: Bull 

 Geol. Soc. America, vol 4, 1893, pp. 313-332. 



"Lawson, A. C, Report on the geology of the Rainy Lake region: Ann. Rept. Geol. and Nat 

 Hist. Survey of Canada, for 1887-88, new ser., vol. 3, pt. 1, 1889, p. 32. 



