750 WALTER HARVEY WEED 
contraction to which it is here subjected in the extremes of tem- 
perature that are so characteristic of the climate, and the chem- 
ical changes made possible because of the opportunity for 
moisture to penetrate the minute cracks thus formed, yet the 
chemical changes themselves, slight as they appear to be, aid this 
degeneration by swelling up as the molecules become oxidized 
and hydrated. 
The analysis shows a remarkably small amount of chemical 
alteration. It is evident, also, that the process is not the normal 
one of ‘‘weathering,” since silica is not lost. The presence of 
sulphides in the rock itself, the proximity of mineral veins, and 
the presence of sulphurous fumes in the atmosphere which would, 
of course, acidulate the rainfall, probably account for this 
abnormal nature of the weathering. Under such circumstances 
none of the constituents of the rock are constant, since they are 
all capable of passing into solution under such conditions. As, 
however, an increase of silica could not take place, this sub- 
stance must either decrease in amount, or remain constant, and 
the analyses can be best compared by assuming it constant. 
WALTER HARVEY WEED. 
