TOBLE LGA TUONS:. Wi PoM 
which are in an undisturbed condition. The Thompson series is 
therefore regarded as unconformably below the Animikie, and is pro- 
visionally correlated with the Keewatin. 
COMMENTS. 
No petrographical descriptions are given of the Thompson slate 
and of the Keweenawan green schists which are said to be similar. 
The essential likeness or unlikeness of such fine-grained rocks as the 
Thompson slates and the Keewatin green schists can only be ascer- 
tained by microscopical studies. The Thompson slates with the 
microscope are seen to be little altered fragmental rocks, while the 
green schists of the Mesabi range are thoroughly crystalline, and in 
many places altered volcanic rocks. Further, the crystalline schists 
of the Mississippi River are not connected by continuous exposure 
with the Thompson slates, and may belong to a different series from 
them. Certainly a much more thorough study of the problem is 
required before it can be considered as probable that Irving was 
wrong in placing the Thompson slates as a part of the Animikie 
series. C. R. Van Hise. 
