THE PRECAMBRIAN ROCKS OF THE CANTON QUADRANGLE I5 



with a greater quantity of biotitic gneisses than are those in the 

 Grass valley, it seems probable that the formations are distinct. If 

 this is true the value obtained here, assuming an average southwest 

 dip of 10 degrees, is laoo feet. This is also a maximum, and is a 

 result, as in section B, of measuring the thickness in a direction 

 parallel to the pitch. The sum of the figures given for the partial 

 sections A — D brings the total up to 7300 feet. 



In a strict calculation, such as is not possible in the present in- 

 stance, account should also be taken of the two limestone forma- 

 tions in the west-central and south-central portions of the quad- 

 rangle, occurring at what would seem to be respectively the summit 

 and the base of the composite section described above. In the for- 

 mer case a broad outcropless swampy valley renders dubious even 

 the presence of the Precambrian formations as surface rock. In 

 the latter, while to be sure the limestone is below the Pyrites- 

 Pierrepont gabbro-amphibolite belt and presumably below the 

 garnet gneiss injection zone, the exact tectonic relations between 

 the two are so obscure that the assignment of this limestone to the 

 same stratigraphic series with the sigmoid garnet gneiss is hardly 

 justifiable. 



Such an estimate therefore as that proposed above, being' based 

 upon a number of isolated sections, which if they were ever continu- 

 ous have been widely separated by igneous and tectonic activity, can 

 be regarded only as extremely hypothetical, and but a rough approx- 

 imation at the best. Finally, while the value given is the maxim^^^m 

 that can be allowed for the Canton quadrangle, the point which it 

 is desired to emphasize is that it is trifling in comparison with 

 the 18 miles recently announced by Adams and Barlow as 

 the thickness of the Grenville-Hastings series of the Haliburton- 

 Bancroft area in Ontario (1910, pages 33-34). In spite of the al- 

 most incredible quantity of clastic material developed in that region, 

 and even allowing for any possibly unrecognized duplication of the 

 formation in whole or in part, it seems quite certain that the strata 

 in that portion of Ontario have a far greater bulk than it has been 

 possible to assign to the Grenville on the northwest flank of the Adi- 

 rondacks. Throughout the periphery of this part of the mountains 

 and in the adjoining lowlands, the probability of a general obscur- 

 ing of the true thicknesses by crustal movements is very strong, and 

 caution is needed in every attempt to estimate the total amount of 

 Grenville material present. 



Areally, as will be seen on examination of the dr;ftless aren of 

 the accompanying geological map (in pocket of back cover), the 



