A. C. Lawson— Geology of the Rainy Lake Region. 477 
ined under the microscope, and the term “ granulite-gneiss ” 
might be useful as a distinguishing term if the granulitic 
character can by more extensive study be shown to be a com- 
mon one. For the present it will be used provisionally as one 
that suggests the contrast that exists between them and the 
granite-gneisses. 
This thick series of mica schists and granulitic gneisses at- 
tains its greatest development so far as has yet been observed 
in the southern part of Rainy Lake, where its thickness in con- 
tinuous exposure, with the strata at low angles which preclude 
the idea of reversed dips, can be measured for a thickness of 
over two miles in a low anticlinal. The series is for conven- 
lence designated the Coutchiching series, from the Coutchich- 
ing Rapids at the head of Rainy River where the rocks are first 
met with on entering Rainy Lake from the west. They are 
very sharply and distinctly marked off from the lower granites 
and gneisses of the Laurentian. The geological contact be- 
tween the Coutchiching series and the Laurentian system is one 
of neither conformity nor unconformity. The break is of an 
entirely different order, and the contact is eminently that of an 
igneous injection or intrusion of the lower through the upper 
rocks. This series appears to thin out rapidly toward the 
north, and on the north shores of the southern part of Rainy 
Lake, in the neighborhood of Seine, Swell, Red-gut and Rocky 
Islet ‘Bays, and on the islands of the lake, it is seen to form a 
trough in which lies folded another higher series of entirely 
different characters. The rocks comprising it are for the most 
part of volcanic origin. They are chiefly black-green, com- 
pact, hornblende schists; softer, less compact, and more fissile 
green schists in which hornblende is the prevailing constituent, 
but with chlorite, calcite, epidote and other decomposition min- 
erals well represented in them; and, in intimate association 
with these schists and interbedded with them, great sheets of 
‘trap’ comprising uralitic diabases and gabbros (often called 
diorites) and other massive altered basic volcanic rocks of less 
determinate characters. These altered traps are sometimes 
quite massive and sometimes schistose to a varying extent, in 
which case the crushed or stretched condition of the rock is so 
clearly displayed in microscopic sections as to leave no doubt 
that the schistosity is due to pressure and to stretching or pull- 
ing forces upon the rock after the assumption of a firm erystal- 
line condition. When the crushing has been excessive the 
original character is often almost or completely obliterated, par- 
ticularly as the comminution of the rock under such forces is ac- 
companied by the development of secondary minerals like 
quartz, calcite, epidote, zoisite, chlorite and albite. Included 
also in this series are dark green, very fissile glossy schists 
