;N'o. 10. — MdamorpMsm of Clastic Feldspar in Conglomerate 

 Schist. By J. E. Wolff. 



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 Archaean 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 pnyllites. 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 Hock-Disintegration to certain Transitional Crystalline 

 Schists. Bull. Geol. Soc. Am., Vol. II. pp. 209-224. 



VOL. XVI. — NO. 10. 



