364 PRE-CAMBRIAN NORTH AMERICAN LITERATURE 
Adams? describes a district of 3500 square miles of pre-Cambrian rocks 
belonging to the Grenville series immediately east of the original Laurentian 
area, described by Logan and Ells, and northwest of the city of Montreal. A 
subordinate part of the area about Trembling Mountain and another area to 
the west of St. Jerome are referred to the fundamental gneiss. The Grenville 
series occupies the major portion of the district, but about 1000 square miles is 
occupied by anorthosite, which occurs in one large area known as the Morin 
area, and tensmaller masses. The Morin anorthosite encloses detached masses 
of the gneiss. There are also present in the district one mass of intrusive 
syenite covering an area of thirty-six square miles, and a much larger one of 
granite in the northeast portion. 
The Grenville series is composed of rocks in well-defined bands, the whole 
exhibiting a clear foliation, usually parallel to the banding. The series thus 
has a decidedly stratified appearance, similar to that presented by sedimen- 
tary rocks. The gneiss which on the west side of the area dips at an angle of 
40°, toward the east become nearly flat, often quite so, and these nearly flat 
gneisses extend to the north and east far beyond the limits of the map. 
Throughout this area of flat-lying rocks, the gneisses with their interstratified 
limestones and quartzites are as highly crystalline as in the most highly 
contorted districts and have evidently undergone an extensive stretching or 
rolling out, resulting in the tearing apart of the less plastic bands with the 
flowing of the material of the more plastic bands into the spaces between the 
separated fragments. : 
Petrographically the rocks of the district are found to fall into four classes: 
1. Anorthosites and granites of igneous origin. All gradations may be 
seen between the ordinary anorthosite and those in which the whole is granu- 
lated so as to resemble in appearance a saccharoidal marble. The whole 
. rock thus moved under pressure like so much dough, its continuity being per- 
fectly maintained. This is Professor Heim’s ‘“‘Umformung ohne Bruch,” 
millions of little cracks taking the place of a few larger ones, and it is by this 
process that granites and many gneisses and other crystalline rocks when 
deeply buried under great pressure and probably very hot, move and accom- 
modate themselves to stresses. This, it will be observed, is quite distinct and 
different from the shearing accompanied by the development of new materials, 
which takes place under other conditions and probably nearer the surface. 
2. Augen-gneisses, leaf-gneisses, granulites, and foliated anorthosites, genet- 
ically connected with the last group, and largely, if not exclusively, of igne- 
ous origingalso. The structural characteristic of this class is the cataclastic 
or granulated one, formed by the mechanical breaking down of the web of the 
rock under movements induced by great pressure, which movements produce 
in the rock a foliation more or less distinct, according to their intensity. 
™A Further Contribution to our Knowledge of the Laurentian (Art. VIL.), by F. 
D. ApAms, Am. Journ. Sci. (3), Vol. L, 1895, pp. 58-69, with Plates I. and II. 
