WP SIMOIDUES IPO iS IUIDIEIN IGS, 
remain which is known as the water of imbibition. The sub- 
capillary pores are conceived to be of sucha size, smaller than 
.00002 centimeter in diameter, as to contain only the water of 
imbibition.” 
As in the case of pores, Professor Van Hise has classified 
sheet openings which occur along bedding, jointing, or other 
fissile planes, as capillary and subcapillary, including in the lat- 
ter all such as are less than .oOOOI centimeter in thickness.? 
The third class of openings consisting of cavities, caves, and 
caverns are a result of the removal of one or more of the 
grains of which a rock may have been originally composed. 
They occur most commonly in limestone or dolomite, although 
present in other less readily soluble rocks. 
Ill. EXTERNAL CAUSES OF DECAY 
In the selection of a stone for any purpose a consideration of 
the climatic conditions under which it is to be placed, is of very 
great importance. A uniform climate in which the temperature 
is always above the freezing point is most favorable to long life. 
A dry climate is conducive to stability, while a moist or humid 
atmosphere promotes decay. A stone which will withstand the 
vicissitudes of a moist, temperate climate, where there are long 
seasons of alternate freezing and thawing, short hot summers, 
and cold winters, must be of the most enduring kind. The well 
preserved condition of the monuments of Rome and other cities 
of the Mediterranean basin, after centuries of exposure, is not 
due so much to the inherent qualities of the stone, as to the 
warm, dry atmosphere. The obelisk of Luxor stood for cen- 
turies in Egypt without being perceptibly affected by the climate, 
but after only forty years of exposure in Paris it is now filled 
with small cracks, and blanched. The same is true of the 
obelisk in Central Park, New York, from which many pounds of 
small fragments have fallen. 
* (bid. 2 Did. 
3A. A. JULIEN: Tenth Census, Vol. V, p. 370. 
4J. C. Smock: Bulletin N. Y. Museum, Vol. II, No. 10, p. 385. 
