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Karthquakes in Sicily. 221 
of cutting, and the cheapness of the tufa, > call cal 
adoption as a building-stone, contrary to the custom 
ancestors, as appears from the immense excavati pits 
about Syracuse, Girgenti, and some others of the eeetent cities 
of Sicily. Till lately, the common cement was composed of 
a fat earth, to which ashes were sometimes added; it was 
called tajo. Within a few years, lime and sand have been 
used. But they do not always employ for lime that stone 
which it hardest and most proper; nor that which requires ~ 
an equal degree of heat in calcination; nor are all the pieces 
white. It is not slaked methodically, nor mingled with that 
patience which caused the ancients to say, that lime should 
be tempered by the sweat of the brow. And here, indeed, 
this labour is the more indispensable, as Palermo is destitute 
of puzzolana, and of those ferruginous earths, which render 
such valuable service to those volcanic towns of the island, 
he soft rock of the surface serves, in large masses, for 
a foundation upon the clay. But the brittleness of the rock, 
and the instability of the earth, its readiness to change froma 
level at the least motion, or by the action of moisture, which 
the air and soil of Palermo make permanent, render the 
foundation very far from firm. I have seen pieces of the 
foundation of large edifices, so entirely reduced to earth, as ~ 
to be removed with a spade. This inconvenience exists even 
when the rock in its natura] situation serves as the base. 
Where a building is raised upon a soil, the parts of which 
are of different natures, it must suffer much from the unequal 
Ser of this soil. The right side of the royal palace, 
as for several years been inclining from a waa in 
consequence of its having been placed on the ancient allu- 
vial formation, while the remainder of the building ee ona 
rock. Sometimes we see buildings raised on an incline 
plane, with one part of the base more elevated than the 
other; in this case, it is evident that the oblique pressure 
is compounded of two forces; one, perpendicular to the 
resistance, and which is overcome by it; the other parallel 
with the resistance, but ae not entering into the action, 
operates in its own direction. The equilibrium is thus de- 
stroyed, and the stability of such buildings cannot be of long 
duration, 
