THE CROWSNEST VOLCANICS. 
31 
DISCUSSION. 
Aside from their exceptional petrographical composition 
these voicanics are interesting from other standpoints. They 
are only one of the few post-Cambrian bodies of igneous rock 
in the great geosyncline of the Rocky Mountain system in 
Canada. Igneous rocks, abundant in the more western Cor- 
dillera, have been found so rarely in the Rocky mountains of 
Canada as to excite particular interest. Farther south, in 
Montana, volcanic rocks, also of alkaline types, occur, intruding 
strata of late Cretaceous age 1 . 
In the Ice River district, British Columbia, are found ultra 
alkalic igneous types also, here consisting of a complex of pluto- 
nic rocks in the form of an asymmetrical laccolith. 2 The age 
of this intrusion is placed as post-Cretaceous, on structural 
and correlation evidence. 
These instances of plutonic and hypabyssa.1 rocks of post- 
Cretaceous date, of similar highly alkaline types, are significant 
when correlated with the mid-Cretaceous Crowsnest alkaline 
voicanics. 
In the well known “Petrographic Province of Central 
Montana” described by Pirsson, 3 the rocks are characterized 
by equal amounts of soda and potash in the most siliceous 
types, with potash increasing in the less siliceous types. Although 
only one analysis of the Alberta rocks is available, the petrography 
leaves no question that soda in this area greatly dominates over 
the potash. As the Crowsnest voicanics form only a single 
occurrence in a localized area, they cannot be considered as 
forming a petrographic province by themselves. Taken in 
connexion with the numerous other alkaline occurrences in the 
Rocky mountains of the United States, many of which are 
referred to in Pirsson’s paper, 4 they serve to extend the alkalic 
J Pirsson, L, V. Bull. U. S, Geol. Survey No. 237, p. 199, and map, p. 20. 
2 Allan, J, A. Geology of the Ice River district, B. C.: Abstract of a 
thesis presented to the faculty of the Massachusetts Institute of Technology in 
partial fulfilment of the requirements for the degree of Doctor of Philosophy, 
1912, p. 4, etc, 
3 Pirsson. L. V. American Journal of Science, 4th ser., vol. 20, 1905, pp.35- 
4 Loc. cit. p. 36. 
49. 
