634 I oH Es VOGT. 
my earlier determination of the rock from Lofoten described above, 
at about 8-9 per cent magnetite. 
We here interject the remark that the simultaneous crystalliza- 
tion of “titanomagnetite’’ and hypersthene, diallage, or olivine, 
taking place at an early stage of crystallization in norites and 
gabbros (with olivine gabbros, etc.) which carry much ferromag- 
nesian silicate and some few per cent of iron ore, explains how 
the well-known magmatic differentiation products of “titanomag- 
netite” in these rocks are characterized by an enrichment of 
““titanomagnetite” plus the ferromagnesian silicate in question, 
consequently hypersthene, diallage, or olivine respectively. 
Magnetite in the granitic rocks——Here the magnetite, when 
present in a quantity of at least o.5 or 1 per cent, commences 
crystallizing at a very early stage, viz., a little later than the 
apatite, which, as is known, often appears as idiomorphic needles in 
the magnetite, but on the other hand earlier than the biotite or 
other ferromagnesian silicates which, in part, were deposited on the 
Fixkor per magnetite. 
At this early stage, however, the whole quantity of magnetite 
was not crystallized. We are thus able to detect exceedingly 
small magnetite individuals in the groundmass, for example, in 
quartz porphyres; and the many analyses (Nos. 14c-29c) of glass, 
ground-mass, and intervening mass between the orbicules, etc., in 
granite without exception show a little Fe,O, and FeO. In the 
granitic eutectic which at last results, there usually seems to appear 
about 1 per cent Fe,O, and FeO, of which, however, a little is 
bound up with the small quantity of ferromagnesian silicate, and 
a little Fe,O, probably also appears as a solid solution in the 
feldspar. The magnetite seems to appear in the final eutectic in a 
quantity of about o.5 per cent. 
For the magnetite as well as for the ferromagnesian silicates the 
solubility is much less in the granitic than in the gabbroidic magmas. 
Spinel.—Magnetite and spinel (pleonast and hercynite) (Mg, 
Fe) (AL, Fe.)O,, with at most about 7-10 per cent Fe,O,, but some- 
times with more FeO than MgO, form between them a series of 
t Foslie (loc. cit.) sets the boundary still somewhat higher. This, however, is 
not in accordance with my investigations of the problem in hand. 
a ee 
