346 Svs Es VOCE 
surplus of feldspar components, the crystallization of feldspar may 
continue without a simultaneous secretion of quartz until the 
eutectic boundary-line between quartz and the feldspar components 
has been reached. When this has occurred, however, a simultaneous 
crystallization of feldspar and quartz commences, with only a 
quite inconsiderable change of the SiO, percentage of the magma 
remnant, while we constantly more and more approach the 
“ternary” eutectic: Qu:Or:Ab+An (with a trifle magnetite and 
ferromagnesian silicate). 
The groundmass in the quartz porphyries and the closely related 
rocks consists, as is well known, in some cases of microfelsite and 
in others of granophyre, and these structural forms indicate a 
simultaneous crystallization of quartz and the feldspar in question. 
The final crystallization consequently took place also with regard 
to the structure at a eutectic or eutectic boundary-line. 
Especially acid quartz porphyries (with more than 75 per cent 
SiO,) show phenocrysts of quartz and feldspar in about equal 
amounts, but groundmasses of normal microfelsite or granophyre, 
that is to say, with relatively less quartz than among the pheno- 
crysts. The groundmass, consequently, here must have grown a 
little more basic than the original rock. I lack material, however, 
to prove this by chemical analysis. 
If we now turn to the deep-seated igneous rocks, we find that 
the quartz-norites and quartz-gabbros (with about x to 5 or 6 per 
cent quartz), the quartz-diorites, the quartz-syenites, etc., pre- 
vailingly show that the quartz first began crystallizing at a 
relatively late stage. As we shall explain later (Figs. 17 and 18) 
when treating of the quartz-norites, this crystallization of quartz 
at a late stage took place, not by itself, but simultaneously 
with the final crystallization of the feldspar (the plagioclase) and 
the ferromagnesian silicate in question. In the granite porphyries, 
which contain but little ferromagnesian silicate and magnetite 
but are especially rich in feldspar, with about 66-70 per cent SiO,, 
the crystallization commenced with the solidification of some 
feldspar. 
The crystallization in ordinary granites usually commenced 
with a solidification of some magnetite and ferromagnesian silicate, 
