244 Canadian Record of Science. 
willemite, v=6'6; for amphibole, 5:9 ; for pyroxene and en- 
statite, 5°5; for chrysolite, 5°4-5°3; and for phenakite, 4°6. 
In the sub-aerial decay of crystalline rocks, while feldspars 
and scapolites among aluminiferous silicates are kaolinised, 
the micas, notwithstanding their laminated structure, are 
much less readily changed; and garnet, epidote, tourma- 
line, andalusite, and topaz are found unaltered with the 
quartz, corundum, spinel, cassiterite, and magnetite left 
behind by the decay of the feldspathic rocks—a process in 
which even amphibole, pyroxene, and chrysolite share. 
“The greater stability of those [silicates] which belong to 
the more condensed types is shown in their superior resist- 
ance to decay, and is thus of geological significance.” 
While the above are examples of the varying resistance 
to the atmospheric influences of carbon dioxyd and water 
combined, other changes less well known take place in sili- 
cates by the subterranean action of watery solutions, where 
a greater insolubility determines the formation of certain 
softer hydrated magnesian and aluminous species by epige- 
nesis from harder and more condensed species. The pro- 
‘duction of these epigenic products, as was said in 1885, is 
due to their “chemical stability under the circumstances,” 
and it was added, “The constancy in composition and the 
wide distribution of pinite show that it is a compound rea- 
dily formed and of great stability.” Such being its charac- 
ter, it might be expected to occur as a frequent product of 
the aqueous changes of other and less stable silicates. It is 
met with in veinstones in the shape of crystals of nephelite, 
iolite, scapolite, feldspars, and spodumene, from each of 
which it is supposed to have been formed by epigenesis. 
Its frequent occurrence as an epigenic product is one of the 
many examples to be met with in the mineral kingdom of 
“the law of the survival of the fittest.” It is, however, 
difficult to assign such an origin to beds of this (described 
as dysyntribite and parophite), which are probably the 
results of original deposition or of diagenesis. 
Mr. EK. A. Ridsdale, who during the present year (1888) 
has done good service by publishing a suggestive essay 
