14 
(ECONOMY 
^nd therefore it is a vulgar miftake, that out? 
anceftors excelled the modern archite&s in the 
art of building as to this point k . 
However ignorant we may be of the caufe, 
why large rocks are every where to be feen 
fplit, whence vail fragments are frequently torn 
off*, yet this we may obferve, that fiffures are 
doled up by water, that gets between them, 
and is detained there ♦, and are confolidated by 
cryjial and ftpar . Hence we fcarcely ever find 
cryftal , but in thofe ft ones , which have for feme 
time in its chinks water loaded with flony par- 
ticles. In the fame manner cryftals fill the ca- 
vities in mines, and concrete into quartz or a 
debafed cryftaL 
It is manifeft that ft ones are not only gene- 
rated, augmented, and changed perpetually 
k Too great ftrefs ought not, I think, to be laid on this 
observation of our author, though it may be in part true ; 
for without fuppofmg that our anceftors had more Ikili in 
building, we may fuppofe, what was likely to be the cafe, 
that they ufed more care in the choice of their materials, 
and had them wrought up with more labor ; which mull 
add conliderably to the lirmnefs of the cement. Where thefe 
circumftances have happened to be wanting, time alone has 
not been able to produce the fame elfedl. I have feen a 
houfe about fourfeore years old, where one might rub out 
d 16 mortar from between the bricks without fcarcely uling 
any force. 
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