DISCOLORATION. 
53 
presence of sap is a serious matter, as the stained edge of each block 
must be split off, which adds somewhat to the cost of production. 
This discoloration has been supposed to be always due to the oxida- 
tion of the ferruginous minerals of the granite, biotite, hornblende, 
magnetite, and pyrite, but the Maine thin sections examined by the 
writer do not bear out this theory. Thus one from the Tayntor 
quarry, near Hallowell, shows that the stain has insinuated itself 
into the cleavage planes and cracks of the feldspar and muscovite 
and in the cracks of the quartz, forming minute deposits of limonite 
therein, but the biotite scales and magnetite particles are generally 
untouched by the stain. A section taken from the " top " of the 
Hopewell quarry, in Sullivan, where the fresh rock has a bluish tinge 
and the sap a general bull' 
color, shows that the stain- 
ing extends along the cleav- 
ages and fissures and in the 
spaces between the miner- 
als, but that it does not 
appear in connection with 
the biotite scales, although 
it is increased by the mag- 
netite particles. A section 
from the upper part of 
High Isle, south of Rock- 
land, where the dark sap is 
an inch wide and an inner 
lighter part is one - fifth 
inch wide, shows a series 
of roughly parallel cracks 
crossing the sap vertically, 
with subsidiary transverse 
cracks. These cracks and 
the cleavages of the feldspar and the spaces between the minerals are 
stained, but the staining has no connection with the biotite, and some 
large particles of magnetite are scarcely touched by it. (See fig. 2.) 
In the outer zone the limonite is darker and probably older and 
thicker than in the inner one. That " sap " is not generally due to 
the oxidation of the minerals of the granite is also probable from the 
fact that no such general discoloration appears on fresh granite sur- 
faces, even after many years of exposure to the weather. 
These observations lead to the inference that the discoloration called 
" sap " is, in the Maine granites, not due chiefly to the oxidation of 
the ferruginous minerals of the granite by " underground water," 
but chiefly to the deposition of limonite by ferruginous surface 
water. The water descended along the vertical joints and then 
Fig. 2.— Minerals in thin section (3.76 by 4.23 millimeters 
=0.15 by 0.17 inch) of biotite granite from High Isle in 
Knox County, showing "sap." The ramifications of 
"sap" (limonite stain) across and around feldspar and 
quartz particles (marked / and q) are independent of 
the biotite and magnetite particles. Fine-lined parts 
are biotite; fine-dotted areas are titanite; large black 
masses are magnetite. Some of the borders of quartz 
particles are shown by dotted lines. 
