THE PRECAMBRIAN ROCKS OF THE CANTON QUADRANGLE I3 



lation of the Grenville of the eastern protaxis with the Kewatin of 

 the Lake Superior region, the practice has been followed in the 

 pages of this report of referring to the Precambrian intrusives of the 

 Canton quadrangle simply as post-Grenville. In this manner the 

 question is left open for the present, and any implications attendant 

 upon the use of the term Laurentian, as understood in the strict 

 sense, are avoided. 



The sediments are of the type usually found in the Grenville of 

 the eastern part of the continent, namely, the metamorphic equiva- 

 lents of sandstones, shales and limestones, with various subordinate 

 modifications and transitional varieties. Biotite schists, garnet 

 gneisses and crystalline limestones, often containing a notable 

 amount of silicates, make up the largest portion, probably 90 

 per cent, of the sedimentary material of the quadrangle. These 

 formations find their greatest development respectively in the west 

 central, southeast and south central portions of the area. The gar- 

 net gneiss, a large mass of which has been injected by successive 

 intrusions of gabbro-diorite and granite gneiss, is of much greater 

 relative importance in this quadrangle than in neighboring Adiron- 

 dack territory, so far as is now known. This is partly accounted 

 for by the thickness of the formation, and in part by the fact that 

 crustal movements have doubled the tilted formation back upon 

 itself at both ends, and thereby increased its apparent areal impor- 

 tance. Besides these three chief rock types, the quadrangle affords 

 a number of others of lesser importance, such as quartzite, quartz 

 schist, quartz-mesh limestone, pyritous gneiss, amphibolites, cal- 

 careous schists, garnetiferous biotite schists and others, which to- 

 gether occupy but a relatively small area. 



If the total thickness of the sediments could be measured with 

 any degree of approximation, it would probably be found to be some- 

 where near 2 or 3 miles. Difficulties are imposed, however, by 

 post-Grenville crustal disturbances, which render it almost impos- 

 sible to find a stratigraphic section of notable length or continuity, 

 or one which is not rendered valueless by the probability of an inde- 

 terminable amoimt of repetition by tight folding. The following 

 composite section will nevertheless serve to show that the thickness 

 can not be very great in comparison with figures obtained in other 

 Grenville areas, as for example in Ontario. 



Section A. The middle limb of the broad sigmoidal belt of gar- 

 net gneiss and limestone in the southeast corner of the quadran.de 

 shows a thickness of 3600 feet, of which a sixth at least should be 

 deducted to allow for the abundant granitic and amphibolitic igne- 



