THE PRECAMBRIAN ROCKS OF THE CANTON QUADRANGLE 89 



little light is thrown on the history of the amphibolite masses, be- 

 yond the fact that in some cases, such as those noted above, they are 

 true inclusions. 



Adams and Barlow have recently made a notable contribution 

 to this subject from their studies carried on in Ontario (Adams and 

 Barlow, 1910, pages 97-110). According to these writers, the 

 actual stages in the contact alteration of limestone into amphibolite 

 can frequently be observed. The normal contact rocks, such as 

 pyroxene-scapolite gneiss, are first produced, and these through 

 elimination of lime and transfusion into them of ferromagnesian 

 components from the granite are further altered into amphibolites. 

 That this is the most appropriate explanation for the contacts de- 

 scribed, there can be little doubt ; but it is a question, as the authors 

 admit, whether it alone can account for the miles upon miles of 

 such material in the heart of the great northern batholiths. 



On the Canton quadrangle the granite-limestone contacts, though 

 they do not completely negative this view in its local application, at 

 least make it appear improbable that the granite has had widespread 

 influence in the immediate transformation of limestone or other 

 Grenville xenoliths into amphibolite inclusions. Observations in 

 various parts of the quadrangle, as noted on a previous page, tend 

 to confirm one's impression of the inability of the granitic invasion 

 uniformly to produce contact phenomena of this character. The 

 general problem of contact action offered by these post-Grenville 

 granite invasions is, however, one which it is impossible to discuss 

 adequately at this stage of investigation. But whatever the extent 

 to which exomorphic alteration may be conceded to have taken 

 place in this vicinity, it is noticeably of far less intensity, and the 

 action of mineralizers is much more restricted, than in most granite 

 intrusions of Postcambrian age. 



At some points, as at Eddy, the association and grouping of the 

 formations strongly suggest that the amphibolite is an extreme 

 phase of local contact alteration of certain strata of the Grenville; 

 but at other and more numerous points the failure to find such an 

 association is strongly indicative of the more usual inability of the 

 granite magma to carry the metamorphic process to its expected 

 conclusion. The general absence in the interior of the granite of 

 inclusions other than amphibolite is one of the most impressive 

 features of Precambrian geology. Occasionally, as east of Pyrites 

 or south of Pierrepont, where peripheral injection zones are devel- 

 oped, garnet gneiss xenoliths are locally abundant; also a small 



