ORES OF IRON 143

dyke. According to Per Geijer (Geol. Kiruna, 1910, p. 269;
he later adopted the dyke theory), the ore was discharged as
a lava flow of magnetite.
One essential fact is the occurrence along the base of the
quartz-porphyry of fragments of all the varieties of the underlying
 ore. The ore was therefore in existence before the first
quartz-porphyry lava flow. Prof. Daly’s theory is attended
by the difficulty that the quartz-porphyry contains only
from 2-9 to 8 per cent. of iron oxide, and the lowest flow,
which could alone have supplied the ore, could not have
provided the quantity in the lode; and that porphyry still
contains a normal amount of iron.

SY. -

QP CST Gi’ ow. ws’

Fie, 46.-—TuE ORE-SHEET OF KIRUNAVAARA, SWEDISH LAPLAND.
Sy.P., syenite-porphyry; solid black, the ore, sharply bounded above,
with occasional secondary spurs passing upward,” Q.P., the quartzporphyry,
 of which the lower flow contains at the base angular
fragments of the ore; C.S.T., conglomerate, sandstone, and tuff; S.,
quartzite.

The iron ore pebbles in the quartz-porphyry favour the
formation of the ore by some aqueous agency. The sheet
of ore (Fig. 46), though sharply separated from the quartzporphyry,
 passes down gradually into the underlying syeniteporphyry;
 the iron appears to have been dissolved from the
underlying syenite and deposited on its surface as a sheet
of phosphatic bog iron in a swamp, as suggested by W. H.
Herdsman (Journ. Ir. and St. Inst., Ixxxiii, 1911, p. 480),
Or as a deposit from hot rising water, as suggested by Bick-Strém
 (Geol. Fir. Stockholm Fork., xxvi, 1904, pp. 180-5),
OF as a sheet of surface ironstone formed by evaporating
water.l Backstrom described the process as pneumatolvtic

as
‘ De Launay, dun. Mines (10), IV, 1903, Pp. pad =
sedimentary, A new paper by Vogt (6G. For. Bork I92 fib 153 5)
Arges the intrusive nature of the ore, regarding the
Segregations,