Adams— Contribution to our knowledge of the Laurentian. 68 
pendent masses but elsewhere are found forming the peri- 
pheral parts of great intrusions of anorthosite or granite where 
the pressure is most intense. In these latter cases there can 
be no doubt concerning their origin, as all possible gradations 
are seen from the massive to the perfectly foliated rock. The 
progress and extent of this granulation is excellently brought 
out in thin sections of these rocks by polarized light. An 
extended description of the action of this pressure and the 
effects produced by it is, however, beyond the scope of the 
present paper. In the massive uncrushed anorthosite, the 
twinning of the plagioclase is well seen and there are no 
pressure effects. The structure is that of an ordinary plutonic 
rock. In the anorthosite near the edge of the mass, however, 
the web of the rock is seen to be breaking down. The 
broken crystal fragments have moved over one another, 
little areas and strings of plagioclase. grains derived from the 
breaking down of the larger individuals are seen between and 
about the latter. The structure is distinctly cataclastic. 
In the distinctly foliated anorthosite from the periphery of 
the area, the rock is seen to be in an advanced stage of granu- 
lation, uncrushed remnants of plagioclase more or less numer- 
ous however still remaining. These possess irregular jagged 
edges and show well-marked strain shadows. Little fragments 
of plagioclase can be seen in the very act of being separated 
from the parent mass. Lines of broken material often run 
through the length of large remnants, in this way dividing 
them longitudinally into two parts, one of which then moves 
over the other. Two remnants or cores are thus produced and 
a much greater surface is presented to the action of the granu- 
lating forces which continue to act until all the remnants have 
been destroyed and a uniform mass of white granulated plagio- 
clase results, resembling an appearance of saccharoidal marble. 
The whole rock thus moves under the pressure like so much 
dough, its continuity being nevertheless perfectly maintained. 
This foliated anorthosite has in fact been selected on account 
of its toughness for the construction of the pavements of 
several of the streets in the city of Montreal near the wharves, 
which from the continued passage of heavy freight are sub- 
jected to especially intense wear. 
This structure is, I believe, the most widespread and import- 
ant one exhibited by the Archean rocks. It gives rise to 
Professor Heim’s “ Umformung ohne Bruch,” millions of little 
breaks taking the place of a few large 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 accommodate themselves to strains. This 
it will be observed is quite distinct and different from the 
