A. C. Lawson—Geology of the Rainy Lake Region. 479 
never been detected the slightest tendency to gneissic foliation. 
This granite is found cutting the Laurentian gneiss in sharply 
defined but irreeular dykes in certain parts of the region, par- 
ticularly in the Northwest Bay of Rainy Lake. -These dykes 
are very frequently associated with “veins” of pegmatite. 
Where exposures are few and isolated there is danger of con- 
fusing these granites with the older granites of the Laurentian ; 
where the country is well uncovered, however, the different re- 
lationships of the two are quite apparent. 
Of still later age is a system of strong, well-defined dykes of 
diabase cutting the Laurentian, Coutchiching and Keewatin 
rocks and the post-Laurentian granites. These, wherever ob- 
served in various parts of the region have a strike of N.W. to 
N.N.W. Their width is generally from 60 to 150 ft., and they 
are sometimes traceable for miles. These dykes have been 
studied microscopically, as have all the chief types of rocks 
occurring throughout the region, and some interesting features 
have been brought to light concerning them which will be 
found described elsewhere. Besides these dykes there occurs 
between Seine River and Turtle Lake, east of Rainy Lake, a 
somewhat extensive mass or boss of very coarse grained saus- 
surite gabbro, concerning the age of which it isonly known that 
it cuts the Keewatin rocks, and is therefore younger than them. 
It is not improbable that it is of synchronous origin with the 
diabase dykes, possibly the plutonic facies of the same rock. 
These later diabases and gabbro have an interesting possible or 
problematic relationship to the trap flows which form so large 
a part of the Animikie and Keweenawan series. 
The rocks of the region or their equivalents appear in their 
eastward geographical distribution in the neighborhood of Lake 
Superior to pass in a folded state under the flat lying beds of 
the Animikie series, the contact being one of marked uncon- 
formity. The Animikie is, according to the prolonged and 
valuable researches of Prof. R. D. Irving, of the United States 
Geological Survey, the geological equivalent of the typical 
Huronian of Logan.* The Animikie or Huronian is, accord- 
ing to the same eminent authority,t distinct from and underlies 
the Keweenawan (Nipigon). Hence the classification of the 
various geological systems or series of rocks in the country 
west of Lake Superior, so far as our present knowledge goes, is 
with reference to their place in the ideal geological column, as 
follows : : 
Keweenawan (Nipigon). 
Huronian (Animikie). 
Keewatin. 
* Monograph V, United States Geol. Survey, pp. 367-386, p. 390. 
+ Op. cit., pp. ibid. 
