WeatJicring of Diabase in Virgi?iia. — Wafson. 359 
fifteen feet below the surface, in order that any effects produced 
by cultivation, might be eliminated. The sample was selected 
with great care, and was taken from several points along the 
cut, at approximately the same depth, and the several portions 
intimately mixed, from which the final sample was obtained. 
The sample showed a medium light yellow colored, finely pul- 
verulent mass, through which was distributed a large amount 
of fine lumpy material. The lumps readily crumbled under 
the gentlest pressure of the fingers, and while generally coated 
over with a staining of iron oxide, and occasionally some man- 
ganese oxide, the general outline of the original fresh minerals 
could be readily distinguished. The feldspar areas were very 
much lighter in color than those of the augites. When broken 
and examined under the microscope a considerable quantity 
of the fresh minerals was recognizable. The appearance of the 
material under the microscope was that of a light yellow col- 
ored spongy mass, made up of fine shred-like grains, with a 
good sprinkling of the partially decomiposed minerals. The 
feldspar areas were filled with a very white looking material 
having all the appearance of a crystalline body, but when ex- 
amined under crossed nicols no extinction occurred, hence 
these were taken to represent an amorphous product resulting 
from the feldspathic decay. 
After repeated digestion of a portion of the decayed rock, 
in a very dilute solution of hydrochloric acid, until all ferric 
oxide had been removed, the mass was seen to be made up of 
an aggregate of medium sized particles of a white material, 
considerably speckled by a darker colored mineral which was 
taken to be augite — a microscopic examination of the leached 
product revealed feldspar centers, highly doubly refracting, in- 
closed by amorphous masses of kaolin. 
Chemical a/ia/yscs a fid their discussion. 
Chemical analyses of the fresh and decomposed rock are 
given in the accompanying tables, which indicate the nature 
of the rock-weathering. By assuming one of the constituents 
in columns I and II as a constant factor, the results given in 
columns III, IV, and V are obtained. 
