364 The A/IUTlCa/l Geologist. December, 1899 
cent, distributed almost entirely between four constituents, 
viz: SiOs equalling nearly one-half of the whole, or 19.73 P^^' 
cent; Al.iOs, 6.16 per cent; CaO, 8.95 per cent; and MgO, 6.28 
per cent. 
The special features to which attention need here be di- 
rected arc: (i), the change in passing from the frtsh to the 
decayed rock is accompanied by a loss of nearly one-half of its 
original constituents, 41.44 per cent. (2), The large assump- 
tion of water — -hydration — which is a natural consequence. 
(3), The disappearance of 43.58 per cent of the original AI2O3. 
This loss in the alumina constituent is in accord with the writ- 
er's* work on one of the Virginian diabases. 
The MgO, CaO and AhOs have sufifered the greatest loss 
among the individual constituents. The figures opposite iron 
in column II would indicate that the change has been accom- 
panied by a complete oxidation of the ferrous to ferric iron and 
its subsequent retention. 
Table showing the total percentage loss for entire rock for each locality. 
I II III IV V VI VII VIII 
SiOz 33-41 21.66 19.73 8.48 20.92 15.04 30.34 17-43 
AI2O3 9. II 1.17 6.16 0.00 3.27 0.00 0.00 0.00 
Fe203 0.00 0.00 0.00 2.42 0.00 9.10 16.64 3-53 
MnO 0.04 0.32 0.32 
CaO 9-71 8.69 8.95 1.83 8.05 9.60 3.46 9.20 
MgO 15-09 3-98 6.28 0.68 5-12 6.83 6.77 4-97 
K^O °-35^ X.56 °-^" °;f '-3-39 '-^^ ^-^^ 
Na.O 2.64^ ^^ 0.50 1.82 \ ^-^^ 1.40 2.17 
PjOg 0.08 
Igni 0.00 0.00 0.00 0.53 4.18 0.00 0.00 0.00 
Loss, per cent.70.31 37.10 41.44 14.93 39-51 43.96 60.12 37.51 
I. Olivine diabase near Chatham, Virginia. Am. GeoL 
1898, 22, 95. 
II. Diabase one mile west from Chatham, Virginia. 
III. Diabase from Mount Holyoke, Massachusetts. Loc. 
.cited. 
IV. Diabase from Medford, Massachusetts. Buh. G. S. 
A., 1896, 7., 355. 
V. Diabase from Spanish Guiana, Venezuela. Quart, 
[our. Geol. Soc, London, 1879, 35, part 2, 586; Bull. G. S. A. 
.*Loc. cit. 
