83 
as the Ottawa gneiss, and by a younger group of intrusive 
anorthosites. 
As may be seen by referring to the Grenville map- 
sheet, the Grenville series occupies only a small percentage 
of the Pre-Cambrian area. It outcrops in long, narrow 
bands from one half to one mile (-8 to 1-6 km.) wide, that 
have a general strike of N. 30° E., although this varies in 
places to north, and even to west of north. That the series 
has been subjected to intense pressure is shown by the 
strong and complicated folding which has taken place, 
and can be beautifully illustrated even in small specimens. 
An example of this is to be seen on the north shore of the 
Ottawa river at Papineauville. The Grenville series is 
composed of gneisses which have the chemical composition 
of clay slates, though now so completely metamorphosed, 
that they retain no sign of their original character. These 
include many areas of black and rusty-weathering gneisses, 
with compositions intermediate between those of sand- 
stones and clays, which probably represent original sedi- 
ments of the Grenville series. Some sillimanite gneisses 
of this type have been examined and proved to be sedi- 
ments. Others have indefinite characters which do not 
allow of a decision as to their sedimentary or igneous origin. 
A few unimportant bands of quartzite are also encountered, 
but limestone is by far the most important member of the 
series. The limestone is very impure. It varies from 
white crystalline marble to brown, and in composition 
from limestone to magnesite. Where the latter rock is 
quarried in Grenville township, the best analyses published 
show not less than 10-:5% of CaCO;. Silicates are com- 
mon impurities in the limestone, pyroxene and phlogopite, 
being the most abundant. All the minerals found in the 
limestone of this district are included in a list of such 
minerals occurring in the Grenville series in the Haliburton 
and Bancroft areas that is given by Drs. F. D. Adams and 
A. E. Barlow [20]. i 
These two geologists have shown that the Grenville 
series, in the above mentioned area, attains a thickness of 
17-88 miles, (28-6 km.), or 94,406 feet (28,782 m.), of which 
thickness 53-35% is limestone. They have also shown that 
the coarsely crystalline limestones or marbles of the series 
have been derived from blue limestones of a normal sedi- 
mentary type by thermal metamorphism attendant upon 
their intrusion by immense batholiths of igneous material 
32224—64 
