THE FORMATION OF DEPOSITS 25
sinter, and chert are magmatic ; the term covers both gps
and aqueous products, and is too comprehensive to be ©
practical value.
A third use of the term magmatic is that of J. E. Spurr
who in his * Ore Magmas’ (1923, restated in 77. Amer.
LM.E. Ixxiv, 1927, pp. 99-115) adopts an intermediate post-
tion; he excludes ores due to magmatic waters, and regards
a large variety of lodes as due to the intrusion of highly
concentrated and dense magmatic residues” allied to peg-
matites., He states that ‘‘ a magma is a solution ’ (1923,
P- 73). His ore-magmas include magmatic waters in which
the material dissolved is highly concentrated. The material
tuptures the rocks and as ‘* veindikes' fills the fissures it
has made. These magmas behave like cement which, when
stay into a foundation, forces its way into rocks in thin
sheets like a dyke.
This view i gold-quartz veins was adopted by T. Belt
(Mineral Veins, 1861) for those of Victoria; and being
interested in his memoir 1 examined many Victorian quartz:
lodes in reference to their origin as igneous intrusions ;
but the lodes seemed due to solutions, which, though hot,
were cooler than even pegmatites, and which rose through
fissures and in places replaced the walls; this replacement
is shown by the passage from pure quartz to the country
through a silicified zone, and by the included masses of rock
being in their original place and having been enclosed by
the growth of quartz around them. The walls have been
altered by impregnation by solution and not baked by 2
molten intrusion; and the tongues in the adjacent rocks
present the aspect of filled cracks and aqueous replacements.
Spurr compares his “ veindikes” to pegmatites, which occur
galore in countries such as Scotland and Kenya Colony,
where ore deposits are deplorably scanty; pegmatites are
associated with such useful mineral as mica, apatite,
kaolinite, and the gems and sparse metallic minerals as of
Hn occur in them; but pegmatite seldom contains workable
metallic ore,
The distinction between molten rock material, magmatic
waters, and Spurr’s Ore Magmas is not easy to define, because
there is no absolute division between molten and dissolved
materials. For practical purposes, however, a solution 1s
