No. 10. — Metamorphism of Clastie Feldspar in Conglomerate 
Schist. By J. E. Wourr. 
In the complex of metamorphic rocks which occupy the region of the 
Green Mountains in Western New England, two rocks are of importance 
from their wide distribution in Vermont and Massachusetts, and their 
striking appearance. These are the metamorphic conglomerate and the 
albite schist. 
Both rocks occur in typical development in Hoosac Mountain in 
Western Massachusetts, exposed to perfection both in place and in the 
great masses of fresh rock removed in the construction of the Hoosac 
Tunnel. Here the conglomerate, representing the base of the Cam- 
brian, rests on the underlying Archean gneiss, with peculiar relations to 
the latter, both as to mineralogical character and structure, whose im- 
portance, as bearing on the origin of certain crystalline schists, has 
recently been stated by Professor Pumpelly.? 
This conglomerate attains a thickness of six to seven hundred feet, 
and is then overlaid conformably by the second rock, the albite schist, 
possessing a great but as yet undetermined thickness. 
Detailed geological and petrographical descriptions of these rocks will 
appear elsewhere, and are not presented here; but the truly detrital 
character of the conglomerate should be stated, containing as it does 
true pebbles of quartz, feldspar, gneiss, or granite in a thoroughly crys- 
talline matrix, and also the necessary detrital origin of the conformable 
albite schist, now entirely crystalline. The latter rock is not confined to 
the axis of the Green Mountains, but occurs abundantly in the fossiliferous 
“Taconic ” region immediately west, associated with limestones, quartz- 
ites, and finer-grained schists or phyllites. The albite occurs in irregu- 
lar porphyritic grains of variable size, dotting the rock with its glassy 
. crystals, often twinned in two simple halves according to the albite law. 
In thin sections it is strikingly clear and fresh, containing in the differ- 
ent specimens inclusions of muscovite, biotite, or chlorite, grains of 
quartz, grains or crystals of magnetite, epidote, rutile, etc., which are so 
1 The Relation of Secular Rock-Disintegration to certain Transitional Crystalline 
Schists. Bull. Geol. Soc. Am., Vol. II. pp. 209-224. 
VOL. XvI. — No. 10. 
