A. C. Lawson— Geology of the Rainy Lake Region. 473 
demonstrate the assumed dependence of pressure on tempera- 
ture. The pressure and temperature cycles, belonging both to 
the diurnal family of the sun, might perhaps trace their rela- 
tionship to their common. ancestor through separate lines of 
descent and neither acknowledge the other as parent. It is 
unsafe to infer because two currents have a common rhythm 
that one has borrowed it from the other; it is always possible 
that they flow by independent courses from a common source. 
Art. XLVI.—Geology of the Rainy Lake Region, with remarks 
on the classification of the Crystalline Rocks west of Lake Supe- 
rior. Preliminary note; by ANDREW OU. LAWSON. 
In the Rainy Lake Region there can be distinguished five 
groups of rock formations which are geologically distinct from 
one another. The petrographical characters of each group are 
peculiar to itself to a great degree; so that a scheme of classifi- 
. cation which takes into account only those conditions of mu- 
tual relationship, as observed in the field, that serve to dis- 
tinguish the different groups with respect to their stratigraphical 
position, age and genesis is at the same time probably the best 
that could be adopted for considering systematically the purely 
petrographical characters of the rocks of this field by laboratory 
methods. The rocks comprised in the first of these groups may be 
arranged in the following scheme in which Rosenbusch’s nom- 
enclature is employed for the non-foliated varieties. With 
regard to the foliated varieties it will be observed that the 
word ‘‘ gneiss” is used simply with reference to the structure 
of the rock independently of its mineral composition. 
Type. Non-Foliated. Foliated. Texture. 
True granite. ' : ; : . 
Granite, Granitite. CSL gS apaa eines 
(quartzose). { Amphibole Granite. Amphibole-granite-gneiss. | Sar eer a 
( Hornblende syenite. Hornblende-syenite-gneiss. ) Usually very 
Syenite. | | coarse grained and 
(quartz ab-{ Mica syenite. Mica-syenite-gneiss. . |} in micaceous vari- 
sent or only | ties of porphyritic 
sparingly Augite syenite. Augite-syenite-gneiss. J aspect. 
present). ; 
The rocks classified thus under two main types, the granitic 
and the syenitic, cannot as yet be separated in the field in such 
a way as to afford a definite suggestion as to their mutual 
geological relations. Geographically it is frequently possible 
to map off the quartzose, usually finer grained: rocks included 
in the two parallel series of the granitic type from the very 
slightly quartzose, coarse-grained members of the syenitic 
