Weathering of Diabase i?L Virgi?iia. — lVatso?i. 361 
ents is in accordance with and proportional to that observed 
by others in the study of similar and related rocks. 
We have in this case, an example of weathering in which, 
apparently, the thorough decay and disintegration of the rock, 
through extensive hydration and oxidation, has been accom- 
plished, with a loss in the original constituents amounting to 
slightly more than one-third of the whole, or 37.10 per cent. 
While the total amount of material removed, 37.10 per cent, in 
solution, in the transition from the fresh to the decomposed 
rock, is probably something above the average for basic erup- 
tives, the character of the decomposition product indicates 
that the change is far from being complete. 
The following tabular statement compares the soluble ma- 
terial in the fresh and partially decomposed rock, and the soil 
of the \"irginia diabases, extracted by digestion in loocc of 
N/"HC1 for three hours, at the temperature of boiling water. 
Fresh rock 
Soluble matter 20.43V0 
Soluble matter* 31.81V0 
Partially decern- Soil 
posed rock 
20.57V0 34-057e 
28.7170 49 -7270 
Calculated loss of /naferial in t/itfresk and par/tally decomposed rock. 
Constituents 
SiO^. . 
AI2O3 
Fe.Oa 
MnO. 
CaO., 
MgO. 
Na=0. 
K.O.. 
Igni . 
Fresh 
Partly 
Calculated amounts saved 
decom- 
posed. 
and lost. 
I 
II 
III 
IV 
V 
Perceat- 
Percent- 
Percent- 
Bulk 
Rulk 
age loss 
age of 
age of 
analysis 
analysis 
for entire 
each con- 
each con- 
rock. 
stituent 
saved 
stituent 
lost 
51.08 
51.00 
2.96 
94.20 
5.80 
23.58 
24.40 
0.55 
97.63 
2.37 
6.85 
7.29 
0.00 
100.00 
0.00 
0.39 
0.46 
9.36 
8.78 
1.07 
88.50 
11.50 
4.95 
4-39 
0.80 
83.77 
16.23 
2.76 
5.38 7o 
*Amer. Geol. 1897, 22, 93, 94. 
