THE STUDY OF ROCKS. '2*7 
much more frequently of that color, and so if a feldspar be 
found of a pure white color, the chances are it is albite, the 
name being derived from the Latin albus , meaning white. 
These three minerals occur in great abundance in New Eng¬ 
land, sometimes in single masses, sometimes a mixture of all 
three, and sometimes a combination of two out of the three. 
If all three are present in a rock it is either gneiss ( pronounced 
?iice ) or granite, the only difference being that the former shows 
a more or less stratified structure, or lamination, while in the 
latter it is wholly lacking. It must be said, however, that there 
is no sharp line of division between these two kinds of rocks, 
for there occur all gradations of structure from the undoubted 
and prominent stratification to the absolute lack of it, so that 
there will often be doubt as to which of these two classes a 
certain specimen belongs. So we have among the doubtful 
cases rocks which may be designated gneissic granite or granitic 
gneiss. If mica be replaced by hornblende then the rock is 
called hornblendic gneiss or hornblendic granite. If the rock 
contains orthoclase and quartz only it is cajled binary gneiss or 
binary granite, depending, as in the above cases, upon the pres¬ 
ence or lack of stratification. If a surface of this binary gneiss 
be polished the arrangement of the constituent minerals is such 
as to resemble in some degree characters in some oriental al¬ 
phabet-, and on account of this resemblance it is often called 
graphic granite. Most of the New Hampshire granite contains 
the light colored feldspar, while the Scotch granite contains the 
flesh-red variety. This is the reason for the very light color of 
the former and the reddish hue of the latter. The Quincy, 
Mass., granite contains hornblende instead of the mica, and in 
consequence appears of a darker color. Granite is very dura¬ 
ble and consequently is much used as a building material. It 
is not indestructible, however, as some similes would seem to 
imply, for the feldspar decomposes when exposed to the action 
of the air and moisture, very slowly in most cases, but surely, 
and that means the eventual crumbling of the entire mass, to 
become a part of the soil. 
