Adams— Contribution to our knowledge of the Laurentian. 69 
studies of the Saxon Granulit-Gebirge was led to believe that 
certain of the Saxon rocks which closely resemble some mem- 
bers of this class, represent altered sediments, on account of 
their resemblance to certain contact products. Further study, 
however, is needed before any very definite conclusions can be 
arrived at concerning these members of the Laurentian in 
Canada. 
It may be said, therefore, without going beyond that which 
the facts warrant, that there are in the district under considera- 
tion at least two distinct sets of foliated rocks. One of these 
comprising limestone, quartzites and certain garnetiferous or 
sillimanite gneisses, represent in all probability highly altered 
and extremely ancient sediments. The other set intimately 
associated with these are of igneous origin, and comprise 
numerous and very extensive intrusions both acid and basic in 
character which were probably injected at widely separated 
times. ‘Those masses which were first intruded and have been 
subjected to all the subsequent squeezing and metamorphism 
are now represented by well defined and apparently interstrati- 
fied augen-gneisses and granulites, others intruded at later 
periods though showing the effects of pressure retain more or 
less of their massive character, while still others, which as has 
been shown, have been injected since all movements ceased, 
are recognized by all as undoubted igneous intrusions. Further- 
more the limestones, quartzites and sedimentary gneisses above 
mentioned are in this area distributed through the Gren- 
ville Series, being met with in various parts of the district, 
occurring at what appear to be various horizons and are sepa- 
rated by gneisses of igneous origin or by great bodies of 
pyroxenic or other gneisses whose origin is yet doubtful, the 
whole being so intimately associated that it has been found 
impossible in most cases to separate them in mapping. 
The Grenville Series therefore comprises certain primeval 
sediments which have been deeply buried, invaded by great 
masses of igneous rocks and recrystallized. They may per- 
haps in some cases have been mingled with these igneous 
masses by actual fusion. The whole complex has also been 
subjected to great dynamic movements. In this way has 
resulted a series of rocks whose original character cannot in all 
cases be deciphered, but which can be recognized as being 
of composite origin, the sedimentary portion representing 
extremely old if not the oldest sediments with which we are 
acquainted. 
McGill University, Montreal. 
