THE PRECAMBRIAN ROCKS OF THE CANTON QUADRANGLE lOI 



as well as the superposition of the general foliation upon it. This 

 latter phenomenon is indeed characteristic of all sigmoidal folds 

 observed within the quadrangle, being found wherever the banding 

 of an injection zone crosses the northeast trend of the foliation. 

 The best example is found at the inner edge of the east half of the 

 Pierrepont sigmoid, where evidently the compression from the 

 doubling back of the garnet gneiss upon itself was at its maximum 

 (see plate 14, lower figure). 



Isoclinal folding has long been held accountable for the per- 

 sistent northeast trend and the almost uniform high northwest or 

 southeast dip of the formations in the northwest Adirondack region. 

 It is extremely improbable, it is thought, that the miles upon miles 

 of superimposed formations represent the original and normal 

 stratigraphic succession of the beds. Tight regional compression is 

 indeed betrayed by the presence of minute crumplings wherever the 

 Grcnville rocks are exposed, but all indications of demonstrable rep- 

 etition on a large scale seem usually to have been obliterated. Pro- 

 fessor Gushing (see Gushing et al., 1910, pages 109-12) discovered 

 traces of some such structure in the vicinity of the Thousand 

 Islands, and it evidently involves a duplicated series of limestone, 

 schist and quartzite. Whether the fold is synclinal or anticlinal 

 could not be ascertained, but for the purpose of the present compar- 

 ison this is immaterial. The axis in any event is horizontal, or 

 nearly so, in spite of the steepness of the beds, and is parallel to 

 the trend of the formations. It is then in this respect that the 

 Pierrepont isocline differs essentially from that described by Gush- 

 ing, and herein will be found its ultimate significance in the oro- 

 graphic history of the crystallines of the Ganton and adjacent quad- 

 rangles. The axis there strikes northeast, but this one is north- 

 west ; that is nearly horizontal, this dips 30 or more degrees ; in the 

 Thousand Islands region, the axis is conformable to the regional 

 strike of the beds, whereas here it is at right angles to it. In short, 

 the directrices of the two systems of folds are at right angles to 

 each other, and although the latter are parallel to each other with 

 respect to the trace of their Hmbs on the surface of the earth, there 

 is a notable discrepancy in their axial orientation for which it is 

 necessary to find an explanation. 



The accompanying series of sketches (facing p. no) has been 

 prepared to show the ideal mutual relations of pitch to strike and 

 dip, to point out the variability of these relations, and to illustrate a 

 possible conception of the origin and development of the kind of 



