366 
The A?net'ica?i Geologist. 
December, 1899 
This is well illustrated, on the one hand, by the granitic 
rocks of the District of Columbia, where Prof. Merrill* found 
that the transformation from fresh rock to soil was accom- 
l)anied by the very small total loss of only about three (3) per 
cent. The alteration in this case, as concluded by Dr. Merrill, 
was evidently physical, attended with but slight chemical ef- 
fect. As an example illustrating the transition from fresh to 
decayed rock, in which the change was in an advanced stage 
and one of true chemical decay, may be cited the Virginia dia- 
base,! where the writer found the large total loss for the 
rock to equal 70.31%. (See column I of table.) The basalt 
from Crouzet, France, column VII of table, shows a loss of 
60. 12 per cent. 
Apart from the chemical analyses of the fresh and decom- 
posed rock, mechanical analyses of the decayed portion of two 
of the rocks represented in the above table, have been made, 
and become quite significant, when taken in connection wath 
the results in the above table. In both cases the analyses were 
made in the laboratory of Prof. Milton Whitney, chief of the 
Division of Soils, Washington, D. C. For convenience of dis- 
cussion they are herewith appended: 
Name 
1. Gravel 
2. Fine gravel 
3. Coarse sand 
4. Medium sand 
5. Fine sand 
6. Very fine sand 
7. Silt 
8. Fine silt 
9. Clay 
10. Loss at no degrees. 
11. Ignition 
Diam. of particles Per cent. 
in mm. 
Above 2 mm. 
n 
n§ 
-I. 
5 - 
25 - 
I - 
OS - 
01 - 
005- 
• 5 
•25 
.1 
■05 
.01 
mm. 
mm.| 
mm. 
mm. 
mm. 
mm. 
.005 mm. I 
.oooimm.l 
Total I I 9976 I 97-53 
42.3 
0.00 
20.66 
0.00 
12.72 
3-21 
9-37 
13-10 
4.97 
15-39 
4.18 
23-49 
I -13 
23-98 
0.37 
4.16 
1.67 
14.20 
0.66. 
1-73 
99.76 
97-53 
*Bull. G. S. A., 1895, 6, 324. 
tLoc. cit. 
JDiabase— Medford, Mass.— Merrill, Geo. P., Bull. G. S. A. 1896, 
7, 352. 
§Diabase — Virginia — Watson, Thos. L., Am. Geol. 1898, 22, 92. 
