Weathering of Diabase in Virginia. — IVatso/i. 363 
Afialyses of fresh andofdecoitiposed diabase from Mount Holy ok e., 
Massachusetts. 
*Fresh IDecom- Calculated amounts saved 
posed and lost 
Constituents I II III IV V 
Percent- Percent- Percent- 
Bulk Bulk age loss ago of age of 
analysis analysis for entire eacli con- each con- 
rock stituent stituent 
saved lost 
Si02 52.68 53.70 19.73 62.54 37.46 
AI2O3 14-14 13.00 6.16 56.42 43.58 
FeaOs ri.95 21.00 00.00 100.00 00.00 
Fe203=i2.83 I 
FeO 1 9-79 
MnO (^0.44 0.19 0.32 26.76 "jz 
CaO 9-38 0.70 8.95 4.58 95 
MgO 6.38 0.15 6.28 1.44 98 
NaaO 2.56 
K2O 0.88 
Ignition 1.60 8.50 00.00 J 100.00 00 
S. and loss 2.76 
Total per cent .... 99.80 100.00 41.44 
This table shows analyses of fresh and of decomposed trap 
(diabase) rock from Mount Holyoke, Massachusetts, made at 
different times, by separate analysts. The percentages lost 
and gained for each constituent, and for the entire rock have 
been calculated on an iron constant basis and introduced for 
sake of comparison. The figures in column II represent an 
analysis of many years' standing, and since it is not possible 
to know how representative the material yielding them was, 
they must be accepted as interesting only as confirmatory. 
The analyses will serve to show the changes which have taken 
place in the transformation from the fresh to the decomposed 
rock. 
Excluding the alkalis, which were not determined in the 
decayed product, the table indicates a total loss of 41.44 per 
*Average of two analyses made by Dr. G. W. Hawes of the com- 
pact trap rock from Mount Holyoke, Mass. Am. Jour. Sci., 1875, 9, 
186. 
fAnalysis of decomposed trap from the east end of Mount Holyoke, 
Mass., made by President Hitchcock. Economic Geology, p. 135. 
JGain. 
