276 Preface to “ The Natural History 
worked by my direction, so filled up and choaked ; and [ catt 
shew some others, which, if neglected for ten or a dozen of 
years, would be choaked up so effectually, and the contents 
would be so consolidated, that it would require an expense to 
open them up again, almost if not fully equal to the first. The 
history or natural philosophy of stony concretions is already ex- 
plained in the second volume of my Essays, and need not be re- 
peated here. 
We find in many places various kinds of spar, of fluor, and of 
agate, formed and forming by water, depositing particles of dif- 
ferent qualities. Some of the bodies so formed are homogeneous, 
andsome compounded. Some of these concretions assume a fine 
smooth uniform texture; others exhibit, when broken, a cubié 
and a tabulated structure; and others again have a coarse and 
homely grain in the inside. 
In some places, the quality of these concretions is calcareous, 
in others siliceous, and in many places ferruginous ; and we fre- 
quently find them containing a mixture of particles of different 
qualities. Many of these acquire degrees of strength and hard- 
ness equal te any of our rocks and strata; and therefore we may 
infer, that the cementing quality is either contained in the mass, 
of matter deposited by the water, or that it is imparted by the 
influence of the atmosphere. 
I am much inclined to believe it is the last; and I am _ per+ 
suaded that the elementary fire of our atmosphere inspissates a 
great many fluid substances in all the three kingdoms of nature; 
and by penetrating their masses, and being detained and lodged 
there, brings them gradually to various degrees of solidity 5 
strength, and hardness. 
Now it is very observable, that the cementing matter which 
fills up the pores and interstices of our rocks and strata,—which 
connects their several parts, and promotes their solidity, strength, 
and induration, has the very same appearance, and is of the very 
er quality, as the various fossil concretions we are speaking 
; but both the stony concretions and the cementing quality of 
es strata contain a greater variety and mixture of “ghte matter 
than we can easily enumerate or describe. 
From these observations we may safely infer, that these vi- 
rious substances of different qualities are now in a dissolved fluid 
state, mixed with water. The various coneretions formed by 
water, issuing into places accessible to the external air, justifies. 
the inference, and proves the truth of it;, and that our rocks 
and strata are cemented and consolidated by similar substances, 
is evident to our senses: but whether the cementing matter was 
eontained in, and blended with the general composition. when 
the strata were first formed, or was afterwards insinuated by the. 
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