Origin of Pegmatite. — Crosby and Fuller. 155 
20 feet ; while Brogger mentions* feldspar individuals more 
than 10 meters (nearly 33 feet) in length. It is, of course, .by 
virtue of the large scale on which the crystallization has ta- 
ken place that the pegmatite veins are not quarried for gran- 
ite, but rather to obtain mica, feldspar, and quartz for com- 
mercial purposes, these and many rarer species for niineral 
cabinets, and tourmaline and other gems. 
Broggerf also points out that coarseness of crystallization 
alone does not "condition the pegraatitic nature of the veins, 
nor is even necessarily present in order to justify the appela- 
tion pegmatitic. It is the habitus as a whole which deter- 
mines this." Nevertheless, this giant granite texture is very 
constant, and clearly, as already stated, the most distinctive 
and essential character of pegmatite. One fact to be specially 
noted is that the coarseness of texture or scale of crystalliza- 
tion is not proportional to the ^ize of the masses, for dikes 
and bosses hundreds of feet wide may be finer grained than 
those 5 to 20 feet wide. Thus the great boss of pegmatite 
forming Mt. Tug, in Orange, 500 feet wide and 1,500 feet 
long, is relatively tine-grained, while, marking the other ex- 
treme, we recall a vein in Groton less than 2 feet wide con- 
taining stout crj'stals of feldspar 20 inches broad. 
Next in order stands the irregularity of both the mineral 
composition and texture. The normal plutonics are remark- 
ably even grained and uniform mixtures of the component 
minerals; but in the pegmatites the principle of segregation 
has evidently had almost unrestricted play, and irregularity 
is the rule. It is difficult to do justice to this somewhat in- 
definite character in words; but every one who has observed 
pegmatites in the field will fully appreciate it. As noted by 
Brogger,]; the finer grained portions of the pegmatite often 
become eugranitic and indistinguishable from the parent plu- 
tonic. 
The order of crystallization of the various minerals in peg- 
matite is the same as for the normal plutonics — tourmaline 
(and other basic species), biotite, muscovite, basic feldspar, 
acid feldspar, and quartz — and equally constant (Fig. 1, PI. 
VII). Pegmatite agrees with the normal plutonics, also, in the 
♦Canadian Record of Science, 6, G7. 
tibid., 69 and 70. 
jCanadian Record of Science, (5, 0-1. 
