22 GOLD AND TIN DEPOSITS OF SOUTHERN APPALACHIANS. 
described at greater length in the section devoted to the occurrence of tin (pp. 31-32). Dikes 
of this rock appear or have been exposed in many places along the Kings Mountain Range. 
They extend in a belt which crosses Lincoln, Gaston, Cleveland, and Cherokee counties, and 
passes beyond the limits of the area concerned in this report. 
The possibility that the various types just described may be members of a continuous 
series has already been stated. Whether such is the case or not, it seems probable from 
the amount of foliation which each has suffered that the types appeared in the order 
described. The first variety is almost always considerably crushed. The others are pro- 
gressively less affected and the fourth variety only here and there gives evidence of having 
been deformed. 
In the description of the granite (p. 20) the opinion is expressed that the gneiss and granite 
belong to the same period of intrusion, were derived from the same magma, and differ 
only in having suffered unequal amounts of squeezing consequent on being erupted at some- 
what different times. It is here proposed to extend this hypothesis still further to aid in 
explaining the origin of the pegmatite. 
Pegmatite of the first variety cuts the granite and suggests at once the conclusion that 
it was a part of the granite magma. The other varieties of pegmatite were nowhere found 
cutting massive granite. In the northwestern part of Gaston County, however, pegmatite 
dikes of the fourth type are abundant in the somewhat gneissic granite, and the impression 
conveyed by the appearance of these dikes is that they are related to the rock which they 
cut. If the granite were not foliated, it might be said without hesitation that the pegmatite 
dikes represent the last phase of the eruption which resulted mainly in the production of 
granite. The fact that the granite is rather gneissic, however, while the pegmatite is 
practically uncrushed, indicates that considerable time has elapsed between the intrusion 
of the two rocks. This would, in general, be sufficient to prove that the two could not have 
been derived from the same magma. In this case, however, it is believed that a particular 
combination of circumstances accounts for the seeming paradox of pegmatite cutting its 
parent granite after the latter had been rendered gneissic. 
If the gneiss is really the earliest portion of the granite magma, which happened to be 
caught in the grasp of expiring dynamic metamorphism, and if the last of the granite was 
late enough to escape nearly all the squeezing — in other words, if the granite and gneiss 
are related — it is conceivable that pegmatite and gneiss can bear exactly the same relation 
to each other as pegmatite and granite- 
It is believed, in short, that the pegmatite — the residuum from the solidification of the 
granite, the last of the material to be ejected in a molten state from the magma reservoir — 
appeared after almost all regional metamorphism had subsided, and, coming from the 
heated interior, where the effects of surface folding were not felt, cut the gneissic and the 
massive granite indiscriminately, except that the gneiss, having been subjected to pressure 
and stress, was probably weaker and allowed an easier access of the material than the 
massive granite. Such a hypothesis, if true, would account for the relation of the pegma- 
tite to the foliated granite and for its greater abundance in that phase of the rock. It is 
realized that this theory is open to the criticism that it is based on an artificial and perhaps 
unwarranted grouping of favorable conditions. But the intimate lithologic connection 
between gneiss and granite and the close relation of pegmatite and gneiss, added to the 
fact that the pegmatite is almost certainly related to some mass of granite, have favored 
the acceptance of this hypothesis. 
PORPHYRY. 
In a few places masses of rock with porphyritic texture intrude the surrounding schists. 
These masses are in all known occurrences closely associated with gold deposits and are in 
consequence much altered. In general they are light-grayish, granitic-looking rocks, of 
moderate grain. Phenocrystic grains of quartz are visible in many hand specimens. In 
the least altered rock from the Brewer mine crystalline individuals of an unknown mineral 
(see p. 90) are easily recognizable. 
