THE PRECAMBRIAN ROCKS OF THE CANTON QUADRANGLE IO5 



ranges, they have undoubtedly had other systems of major deforma- 

 tion superimposed upon them, which may or may not have coincided 

 with the first in direction, and which may conceivably have given rise 

 to the peculiar features represented in the Pierrepont sigmoidal 

 folds. The northwest-southeast compression seems to have been a 

 dominant and perhaps a recurrent force in the Canton area, and the 

 latest of those operative to any recognizable degree in this vicinity. 

 It not only oriented the axial planes of the compound isoclinal, but 

 also impressed upon it a system of minor crenulations and a regional 

 schistosity parallel to them. These features are without doubt to 

 be correlated in a broad way with the general character of the tec- 

 tonic activity operating in Precambrian times in the region of the 

 southern margin of the Canadian shield. The larger features of 

 this border, such as the infolded sedimentary outliers of the Lake 

 Superior and Temiskaming provinces, and the Grenville complex of 

 the St Lawrence province, have in common a northeast orientation, 

 whose remarkable generality is not minimized by minor deviations 

 due to intensified local igneous activity, and whose significance in 

 the history of Precambrian crustal displacements it is difficult to 

 overemphasize. 



It is not meant to imply, however, that the disturbances which 

 produced such a tilted isocline as that described in this report were 

 necessarily distinct in time or direction, though this is difficult to 

 disprove. Various stresses acting simultaneously could have re- 

 sulted in a deep-seated torsional strain, whose end-product would be 

 the same as that caused by a succession of distinct and discordant 

 compressions ; in this event, the rotating force could be of wholly 

 subordinate nature as compared with that extensive mountain- 

 building activity which impressed a common orientation upon the 

 entire protaxial margin. Granting this to be so, however, an under- 

 standing of the process is so facilitated by analyzing the pressures 

 into their components, somewhat after the principle of the parallel- 

 ogram of forces, that the simplification proposed seems justified. 



With regard to the dip and strike relations of folded beds in gen- 

 eral, and of these to the pitch of the axes, some interesting facts are 

 brought out by a study of the diagrams, which are substantiated by 

 field observations in this and other regions. In all cases the curved 

 line represents the trace of a single outcropping stratum. In figj-ures 

 23 and 24 the outcrops of the limbs are either convergent or diver- 

 gent, but in figure 25 and those following, where the isocline is devel- 

 oped, they are necessarily parallel. In figures 23 and 24 the case 



