THE PRECAMBRIAN ROCKS OF THE CANTON QUADRANGLE 10/ 



accidentally applied to the two widely dissimilar features which 

 seem, on the basis of the evidence presented above, to be genetically 

 related. In fact, as illustrated by the diagrams, the passage of axes 

 of open horizontal folds into steep-dipping axes of compressed and 

 tilted isoclines, and the gradual affiliation and coincidence of these 

 with the direction of mineral elongation produced under strain and 

 recr}^stallization, seem only natural, for in the last analysis these 

 features, both the axes of folds and the elongation of mineral 

 groups, indicate the direction of least resistance and easiest escape 

 from pressure. 



Whether this mutual relationship necessarily follows in all cases 

 on prolonged, deep-seated deformation of a region is not certain, 

 nor indeed probable, but that it is so in the case of the Pierrepont 

 sigmoid is a matter of easy compass observations in the field. Here 

 the pitch of the individual mineral groups in the gneisses, and the 

 pitch of the secondary structures, whatever their size, into which 

 they have been deformed, are fairly constant and coincident. This, 

 for the area studied, seems to be a general relationship, corollary to 

 that proposed by T. Nelson Dale, which holds in effect that the hand 

 specimen is the epitome of the mountain (Pumpelly et al., 1894, 

 pages 157-58)- 



The one remaining tectonic feature which needs to be considered 

 here, is the relation of the igneous bodies to their^ country rock. 

 The gabbros and amphibolites were intruded to a very large extent 

 as sills or dikes parallel to the foliation. Except in the vicinity of 

 Pyrites, where the gabbro has a shape roughly suggestive of a boss 

 or plug, the basic intrusive is a long, narrow sheet of irregular 

 thickness. In its western half it cuts through the limestone mem- 

 ber of the Grenville; in its eastern part it bifurcates, and on becom- 

 ing involved with the garnet gneiss, frays away through the develop- 

 ment of innumerable smaller sheets and sills which form in reality 

 an immense injection zone. The whole mass, together with its 

 country rock, has been thrown back upon itself by the development, 

 as already pointed out at length, of several acute isoclinal folds. 



On the whole, the granite seems to have very nearly the same 

 structural relations as the gabbros. This is best shown in the south- 

 east corner of the sheet where sills of granite of varying size are 

 seen frequently interspersed in the garnet gneiss and amphibolite, 

 forming a true" injection zone with fhe latter. Their parallelism to 

 the borders of the sigmoid and to the banding within it, establish the 

 age of the granite as earlier than, or contemporaneous with, but not 



