THE 
AMERICAN GEOLOGIST 
Vol.]. APRIL, 1888. No. 4. 
NOTES ON SOME DIABASE DYKES OF THE RAINY 
LAKE REGION. 
BY ANDREW C. LAWSON, M. A., 
Geologist to the Geological Survey of Catiada: 
The most recent of the crystalHne rocks of the Rainy lake 
region are comprised in a series of strong dykes of comparatively 
fresh diabase which are observed to cut, at different localities, 
the various members of the Archaean.complex of formations. 
These dykes are not infrequent throughout the country lying 
between the eastern confines of the first prairie steppe, which 
forms the basin of the Red river of the North, and the western 
border of the area of Animikie and later formations of the lake 
Superior basin. Their occurence and some of their characters 
are briefly referred to in my report on the Lake of the Woods 
region.^ As there observed, the occurence of these dykes cut- 
ting the older folded rocks, which in their eastward geograph- 
ical continuation, pass under the flat-lying Animikie and Ke- 
weenawan formations, is suggestive of their possible connection 
with the bedded traps that form so large a part of the two lat- 
ter geological series. With the question of the possible identity 
of character and age of these dvkes with the traps of the An- 
imikie or Keweenawan, or of both, is associated the equally in- 
teresting one of the extent of the earth's surface, over which, in 
early geological times, wei'e in simultaneous operation, those 
particular volcanic forces which appear to ha\'c had their focus 
in the lake Superior basin. 
The more notable field characters of these dykes are: their 
' Geological and Natural History Survey of Canada; annual report, 
1885, p. 41 CC, p. 47 cc. 
