RELATIONS OF THE KEWEENAWAN AND HURONIAN ROOKS. 409 
and possibly also by an intervening period of alteration and folding. The 
Huronian sediments are metamorphic, whatever the nature of the meta- 
morphosing process may have been—and the metamorphism has always been 
greatest where the folding has been greatest—while the Keweenawan sedi- 
ments are unaltered. The metamorphism and folding may have taken 
place before or during the period of Keweenawan eruptions and depositions, 
or both. Our present knowledge of the Huronian is too incomplete to 
allow of a very firm opinion as to this point. 
On ees SS 
