256 The Americdii GeoUxjisI . October, 1896 
ior tliese cracks^ and fisssui-eh; might be produced by strains 
within tlie mass incident to shrinkage on cooling.* 
The notable absence of inclusions in the feldspar "augen" 
would seem to exclude the idea of their formation b}^ segre- 
gation. The presence of granoph^n-ic structure, which has 
been noted in a few cases in the Bedford ''augen"-gneiss, does 
not throw much light on the genesis of the rock, as granoph,y- 
ric structure can no longer be looked upon as necessarily 
denoting igneous origin. (See Hobbs' paper previously 
quoted.) The extreme to which the dynamic action has been 
carried locally is shown by the granitic phase of the rock on 
the southeastern border of the area, where the gneiss has been 
so crushed that none of the "augen" are left. 
The origin of the Bedford i)egmatite veins is equally inter- 
esting. Pegmatite veins are not at all unusual in other lo- 
(ralities, and are probably much more plentiful than the records 
show. There are many of these occurrences in Westchester 
county, and along the Connecticut shore of Long Island sound. 
Pegmatite veins of great size are mentioned by J. F. Kempj- as 
occurring in gneiss near the contacts with gabbro and anor- 
thosite, in the Adirondack region. Granitic and pegmatitic 
veins are also noted by Cross as cutting peculiar schists at 
Salida, Col.]; Those which have been described by L. G. 
Westgateg from the New Jerse}^ highlands, are apparently 
considered by him to be igneous. 
Other marked occurrences are at Portland and Branch ville. 
Conn.; Dillsboro, N. C. ; || Brandywine Summit, Pa. ;^j and 
Blandford, Mass.** 
A valuable contribution on the origin of pegmatites has 
just been published b}^ Mr. G. H. Williams in his ])aper on 
*Regarding the amount of shrinkage in cooling, J. Beckenkamp 
(Zeitschr. fur Kryst. u. Min. V, 461, 1881,) gives the coefficient of cubical 
expansion for orthoclase as .00129 for 60°C. According to this, and 
assuming the orthoclase to have been heated to near its fusion i)oint, 
viz. about r200°C., it would shrink about 2.5 per cent, in cooling. This 
would probably be sufficient to cause strains with resultant cracks. 
Under conditions of great pressure the temperature might far exceed 
1200''C before plasticity could occur. 
tBull. N. Y. State Mus., vol. in, Nov. Uth. 180.'}. 
jProc. Col. Sci. Soc, Jan., 1893. 
§Ann. Rep. N. J. Geol. Surv.. 1895. 
i|J. A. Holmes, Trans. Amer. Inst Min. Eng. vol. xxvi. 
IfRept. of Prog., Pa. Geol. Surv., 1885. 
**W. O. Crosby, Technol. Quart., 1890. 
