THE CROWSNEST VOLCANICS. 
15 
and possibly leucite.” He comments on the amount of analcite 
in the tuffs, and discusses the primary origin of the mineral. 
Analyses of analcite, and of blairmorite-tuff accompany his 
paper, and will be referred to later. 
PRIMARY ROCK TYPES. 
Introduction . 
The mineral composition of a pyroclastic rock may or may 
not closely represent the composition of the pyrogenetic rock 
or magma from which it was derived. In proportion as the 
component minerals differ in specific gravity, original size, 
degree of comminution and reassortment, the resulting tuff or 
agglomerate will tend to differ from its parent magma. In 
drawing conclusions as to the constitution of a magma from 
its representation as tuffs or agglomerates, these and other facts 
should be borne in mind. Stress should be laid on primary 
rock types occurring as fragments in breccias, and on mineral 
associations constantly recurring in the clastic rocks. Occasion- 
ally pyroclastic rocks may simulate the appearance and com- 
position of their parent pyrogenetic rocks very closely, and one 
or two instances of this kind have been noted in the present 
suite of specimens. 
The primary rock types represented either by hand speci- 
mens of fragments from the agglomerates, or by smaller frag- 
ments recognized in thin sections, may be classified in the order 
of their abundance as trachytes; analcite-bearing rocks for which 
the name blairmorite is adopted, and latite. The tinguaite of 
Knight has not been noted by the present writer , 1 while the 
latite was not described by the former author. The minerals 
noted in the specimens include those mentioned by Knight with 
the exception of acmite, anorthoclase, diopside, and horn- 
blende. Beside these, soda orthoclase (anorthoclase of Knight ?) 
magnetite, and oligoclase have been noted, and also secondary 
quartz. 
^night's description of it is added for completeness. See p. 19. 
