156 'The American Geolocjist. March, istn 
approxiinatply idioiiiorpliic character of the earlier crystalliza- 
tions, the quartz being always uUotrioniorphie. In the vugs 
and pockets of the pegmatite veins, however, the order of 
crystallization is reversed, except for tourmaline and other 
ultra-basic species, and the quartz is idiomorphic. This re- 
verse order is well shown in the abundant association of albite 
and muscovite in the pockets of the pegmatite veins of Gro- 
ton, Orange, Grafton, and other towns. The albite occurs as 
distinct tabular crystals (clevelandite) projecting into the 
cavity: and implanted on the albites are the muscovites. 
Notwithstanding the lateness of the crystallization, the quartz 
not iin frequently forms immense vitreous masses (Fig. 2, PI. 
VII), and these often pass into veins of quartz, or quartz and 
accessory feldspar, intersecting the normal pegmatite as well 
as the country rock (Fig. 3, PL VIII), thus testifying clearly 
to the extremely acid character of the magma residuum. 
Rosen busch has sagaciously correlated the pockets and 
druses with the miarolitic structure of the normal plutonics 
— a feature of like significance, but developed, like the crys- 
tallization, on a grand scale. Evidence of contemporaneous 
crystallization is abundant in all the larger masses, the crj^^s- 
tallization of the later species having Ijegun before that of the 
earlier ceased. It is sufficient to merely mention the unique 
example of this which we have in graphic granite. A ten- 
dency to this regular intergrowth of quartz and feldspar is 
frequently manifested ; but it rather rarely attains to its 
ideal development. The perthitic intergrowth of the feldspars 
has, apparently, a like significance. When the earlier crys- 
tallizations assume slender, prismatic forms, as is notably the 
case with tourmaline, the subsequent hardening and crystal- 
lization of the silica (quartz) involves not only the inclosure, 
but also the distortion and breaking of the guest crystals. 
Structure. — It is among the varied structural phases of peg- 
matite that aqueous and igneous characters — the features of 
veins and the features of dikes — are most perfectly blended. 
The pegmatite masses, like true dikes, are frequently fine- 
grained next the wall, becoming rapidly coarser toward the 
center. Where the inclosing formation is the parent plutonic, 
the fine-grained portion, as previously noted, sometimes be- 
comes eugranitic and grades into the wall-rock without any 
