NORTH AMERICAN GEOLOGY. 227 



igueous rocks ofteu liigllly metamoii)hoseiL* The rocks are massive 

 in the center of this belt, but the outer portions have '' been enormously 

 compressed, folded, and faulted, with the result of producing a tough, 

 banded, porphyritic fluxion gneiss, identical with the milonite of Lap- 

 worth or the sheared gneiss of Peach and Hurne. So perfect is the 

 fluxion structure that the rock resembles a rhyolite. As in the banded 

 granulite of Lehmann, elongated feldspar eyes lie in flowing streams of 

 biotite grains and broken quartz, the streams ofteu parting and again 

 meeting arouud the porphyritic eyes. Occasional crystalline eyes of 

 hornblende remain, but most of it has been converted into biotite. 



A point of especial interest is that the feldspar of the eyes is quite 

 colorless and free from inclusions, like the sanidine of recent lavas; 

 while, on the other hand, the feldspars of the inner and massive jiortions 

 of the zone, out of which this outer portion has been reformed by 

 pressure fluxion, are full of inclusions and have the dusty appearance 

 so common in ancieut feldspars. The fresh-looking feldspar eyes have 

 therefore very possibly been subsequently formed as the result of a 

 recrystallization of the old material under the influence of pressure 

 fluxion. In similar manner the biotite has been made out of the old 

 hornblende, garnets have been developed, and quartz has been granu- 

 lated and optically distorted by pressure. Associated Cambrian strata 

 with Scolithus stems shows evidence of the great pressure, and its 

 stems and pebbles are pulled out and flattened. Other localities are 

 found showing various phases of lamination by pressure, and it is ex- 

 pected that further study will reveal more.* 



• 110. Another paper bearing on the same subject is one by Lawsou, 

 entitled " Some Instances of Gneissic Foliation and Schistose Cleavage 

 in Dikes and their bearing upon the Problem of the Origin of the Ar- 

 chean Rocks," Its author describes a number of granitic and dioritic dikes 

 in the Lake of the Woods region in which schistose structure is devel- 

 oped parallel to their walls, and it is thought these instances prove con- 

 clusively that gneissic foliation is not a proof of bedding. Upon this 

 premise it is suggested that the gneissic rocks of the Laurentians and 

 elsewhere may not be sediments metamorphosed in place, but intrusives 

 in which the foliation was induced by pressure, and that their pucker- 

 ings and crumplings raa^^ be due to the increase of bulk during the 

 crystallization process. To account for the lamination and alternation 

 of beds in the younger gneisses it is supposed that they were under less 

 pressure and .more liquid, so that their materials could separate into 

 zones determined by specific gravity and melting points. t 



111. In a paper on supermetamorphism Comstock calls attention to 

 instances in the San Juan district where Silurian and Devonian beds 

 grade into a granitic rock which is underlain by quartzite. J 



'Report (Trans., pp. 1029-1030). 



t Canadian Inst. Proc, vol. 22, pp. 115-128. 



tAm. Naturalist, vol. 20, pp. . 



