154 The American Geologist. March, i897 
The same slow process which builds the giant crystals of 
spoduiiiene, beryl, etc., must tend to gather the materials from 
a large volume of magma. In other words, although in the 
number and variety of the accessory minerals the pegmatite 
veins far exceed the known species of the normal granites, 
we have good reason for believing that in these rarer or acces- 
sory, as well as the more abundant or principal minerals, the 
two types are essentially similar if not almost identical, or at 
least that bulk analyses would show a substantial agreement 
in chemical composition. Substances which are so sparingly 
and thinly diffused in the normal granites as to be almost in- 
appreciable are, if not actually concentrated in the pegmatite, 
developed in a more concrete and tangible form. 
Texture. (Crt/stallization.) — Undoubtedly the most dis- 
tinctive and striking feature of the pegmatites is the crj^stal- 
line structure, which is, in general, on a remarkably coarse or 
gigantic scale, and unparalleled among the sedimentary and 
normal igneous rocks. Well formed crystals of feldspar and 
mica, and even of such rare accessories as beryl and spodu- 
mene, from 6 inches to a foot or more in diameter, are normal 
occurrences. In fact, as regards the size, perfection, beauty, 
and variety of the specimens which they atford, tlie pegma- 
tites are, more than all other rock formations taken together, 
the great repositories of crystallized silicates, as every good 
mineral cabinet testifies : audit is thus easy to understand 
why the pegmatite veins are objects of the highest interest to 
students of mineralogy. An examination of the mineral lo- 
calities of New England and Canada, not to take a broader 
view, would undoubtedly show that a very large majority of 
the most interesting occurrences are in acid or basic pegma- 
tites. 
The maximum crystallization is indicated by the great 
beryls from a foot to a yard in diameter in the mica mines of 
New Hampshire, the largest known example of which is in the 
Museum of the Boston Society of Natural History, and the 
gigantic spodumenes from 10 to over 30 feet in length, and 
from a foot to a yard in diameter, in the tin mines of the 
Black Hills. In the pegmatites of New Hampshire we have 
frequently observed feldspars ten feet or more in length, and 
one crystal in the American mine in Groton measured fully 
