48 The American Geologist. Juiy, wns 
would be raised by the muscovite and sillimanite attached to it, 
the presence of a fehlspar lighter than quartz is shown. 
A portion of one of these pseudomorphs has been analyzed 
quantitatively by Dr. W. F. Hillebrand in the laboratory of the 
U. S. Cleological Survey, yielding the following proportions: 
SiO^ 76.32 
AUU3 15.87 
Fe^Og .53 
FeO .36 
C'aO .26 
K,0 4.55 
Na,0 .24 
H3O at 100" ,20 
HoO above 100 2.01 
AVith traces of TiOg, SrO, Li.O and P,Oj 
100.34 
In conversation with Prof. B. K. Emerson in 1891, he ex- 
pressed his opinion that the nodules were pebbles. I have since 
been convinced of this from examination of them.* 
The greater part of the quartz I look upon as original in the 
rock from which the feldspars were derived, and as essentially 
pegmatitic. The manner of occurrence of the quartz in areas 
quite regularly distributed in the mica, and the high acidity of 
the nodules seem to indicate this. The mica and fibrolite are 
regarded as due to a secondary alteration of a potash feldspar by 
dynamo-metamorphic agencies accompanied by a separation of 
quartz. The alteration of alkali feldspar into microscopic mus- 
covite and quartz is very common. 
During the summer of 1891, I visited the region northwest 
of the Norfolk quarry in company with Prof. Emerson. We 
succeeded in finding similar nodules in place in the Cam- 
brian gneiss of Tobe,y hill (about two miles northwest of the 
quarry), from which outcrops the l>locks have probably been 
derived. 
University of Wisconsin, Madison, May 6, 1892. 
*Mr. J. E. Wolff has shown that the rounded porphyritic feldspars, 
which are characteristic of the "metaraorphic conglomerate" and "albite 
schist" of Hoosac mountain and other localities in northern Berkshire, 
are of detrital origin. (Metamorphism of Clastic Feldspar in Con- 
glomerate Schist, Bull. Mus. Comp. Zool., Harv. Coll., xvi. No. 10, pp. 
173-183.) See also Pumpelly, The Relation of Secular Rook-Disintegra- 
tion to certain Transitional Cr^'stalline Schists. Bull. Geol. Soc. Am., 
ir, pp. 209-224, 
