298 The American Geologist. November. is97 
Tourmaline . .3. —3.24 
Pvrite 4.9 —5.2 
3.— 2.661 34.66 
Ciilcite? .... 2.72 
2.661—2.642 25.02 
Andesine-oli- 
fjjoclase . . . 2.645 
Quartz 2.65 
2.642—2.58 7.60 
? 
Below 2.58 11 .43 
Orthoclase . . .2.54—2.56 
Microcline . . .2.56 
Kaolin 2.34—2.57 
100.00 
Here we have good evidence of the heterogeneous eharactei' 
of the grains in the specific gravit}^ detei-niination, since only 
a possible trace of calcite falls under the division 3. to 2.661, 
which includes a third of the whole. This is probably due 
to the altered condition of the feldspars — the included epi- 
dote, zoisite (and apatite?), etc., increasing the weight above 
2.661. Similarly, the portion which fell between 2.642 and 
2.58 must be chiefly andesine-oligoclase lightened by included 
kaolin. 
On account of this altered cliaracter of the rock, only the 
roughest estimates of the constituent mineral percentages can 
be made. Basing it mainly upon the fairly accurate deter- 
mination of the biotite, we would have: 
Orthoclase 18.00 
Andesine-oligoclase 16.00 
Biotite 12.00 
Microcline 12.00 
Quartz 12.00 
Hornblende 10.00 
Epidote 7.00 
Kaolin 5.00 
Apatite 4.00 
Zoisite 3.00 
Sphene 2.00 
Tourmaline, pyrite, calcite and muscovite 1.00 
100.00 
The structure of the rock is typically granitic, both nmcro- 
scopically and microscopically. The specimens studied are 
considerably altered, but only microscopically. The rock Jias 
suffered severe pressure, with a twisting or crushing move- 
ment at some time. When it last solidified it doubtless con- 
