258 The Americ((n Geologist. Oetoiwr, ix9S 
rill- )i(»t;il)l(' ;il)seiice ot" small crystals of holli (|iiartz ami 
IV'ldspar ill the Bedford jjegruatite would favor a ciu'inical 
rather than an igneous origin. The occurrence of large or- 
thoclase crystals at South Ljnue, Conn., would also indicate a 
chemical origin for the pegmatite veins of that locality, and 
it is not unreasonable to assume a similar origin at the two 
])laces. One of these large orthoclase crystals from South 
Lyme, collected and described by ^^^ T). Matthew, measured 
f)^ by 4^ inches.* 
It will be noticed from the ma[) that the pegmatite veins 
generally occur parallel to the strike of the "augen"-gneiss* 
which would be natural if we assume a vein formation, the 
solutions having followed pre-existing fissures or lines of 
weakness. They also seem to have permeated the wall-rock 
somewhat, thereby causing a gradual transition from the vein 
material proper to the "augen"-gneiss. In only one instance 
was a sharp contact noticed, see p. 243 giving account of L. 
McDonald's quarry. 
The pegmatite veins are evidently of later origin than the 
"augen"-gneiss, for sections of both the granitic and graphic- 
granite type show the minerals to be in their normal condition 
without any signs of dynamic action, which would ap])ear if 
they had been subjected to the same metamorphisiu as the 
surrounding area. 
It seems improbable that the theory advanced by ( Joodehild 
for the formation of pegmatite veins, namely tiie release of 
pressure and segregation from a fused mass, could apply to 
the Bedford pegmatites, which show exceedingly coarse struc- 
ture. Goodchild's theory, however, accounts very well for 
the gradual i)assage of a pegmatite into the surrounding rock. 
That the diorite dikes are intrusives, subsequent to the 
metamorphism of the "augend-gneiss, seems to be proved by 
the fact tliat the component minerals do not show any marked 
dynamic action, and no proof of the hornblende being para- 
morphic after augite has been discovered. 
Mineralogical Laboratory of Columbia Universitij, July, isix;. 
♦Contributions from the Min. Dept., Columbia University, vol. vi. 
No. 2. 
