GRANITE ROCKS OF BUTTE, MONT., AND VICINITY 749 
tint. In the still more altered rock, and in the sands formed by 
its crumbling down, the white minerals are stained by iron rust. 
In the rock analyzed the biotite is partly fresh and unaltered, but 
many of the grains are dull and lusterless, and others are altered 
to green chlorite; more rarely the cleavages are coated by iron 
rust. The hornblende shows the most alteration. Some of the 
grains are fresh, but most of them show masses of ocher, and 
are penetrated by films of it along cleavages and the grains all 
show more or less chlorite as the first stage of alteration. These 
changes all indicate simple hydration and oxidation of the rock, 
and should accordingly be revealed in the analysis. The fol- 
lowing tables show (1) the average composition of the fresh 
rock, (II) the composition of the disintegrated material, (III) 
the percentage of each constituent lost, (eDN/3) the percentage of 
each constituent gained. 
Constituents I II II Vie ere oie 
error of analysis 
SHNCE Sedo or s5|04-03 65.14 +1.01 1.41 3 
Titanic oxide...| .60 59 —0.01 
Alumina. .!5... 3 15.58 15.63 +0.05 0.32 
Herricoxide, 3. ..)| 0.90 2.37 0.51 oT 
Ferrous oxide...| 2.83 2513 —0.70 15 
Manganese oxide] .1I1 tis Onli 100. 10. 
BTM ese atsresiietanens 4.20 3.62 —0.58 14.09 I 
Magnesia ...... 2eris 1.85 —0.30 14.23 7) 
Botashevncrce ws. 4.11 4.29 +0.13 4.04 2 
SOda ttc pra ct oes 2:76 2.63 —0.13 9.51 2 
M oisture com- 
bined espera. 73 apis +0.02 
Moisture below .96 
TT Os, otenentsiers PA) 5ey7/ +0.14 
Bary tavctsesetena ae .07 .I0 +0.03 
SUrOMELA ves eee C4 tr. —0.04 
Phosphoric acid.| .18 .16 —0.02 
99.86 99.08 
The fresh rock contained a little Cl, 0.17 per cent., the dis- 
integrated rock none. The fresh rock held 0.06 per cent. S (as 
pytite), the altered reck 0.05 per cent. SO . 
While the changes in the character of the rock are largely 
physical, and its degeneration, due to the rapid expansion and 
