JOO 
A SYSTEM OF 
SECT. XCIL ■ 
Observation on Clays in general. 
Thofe who have taken upon themfelves tq 
examine the mineral bodies according to the 
principles upon which this Syftem is built^ will 
readily, I hope, exciife thofe faults which may 
have been committed in clalTnig the clays •, be- 
caafe they muft well know, not only how cliffi- 
cult it is to procure a number of different va- 
rieties of this order in their natural ffate, which 
have not been previoufly walked or prepared for 
while I have in dry funimers obferved on the iea-fhore,, that a 
perfed iron vitriol has been growing out of the mud, clays, 
and. vegetables not yet rotted, which has been thrown up 
there together. 
When this opinion is once proved to he true, one may ven- 
ture to go farther, and endeavour by obfervations and ex- 
perinients to prove likewife, that in the fubyerhons or changes 
that the earth has more than once fuifered in every part of it, 
and in which water has contributed the moil: to carry off the 
particles, and to change the ilrata, the clay has been gathered 
•together, and lodged in beds together with other fubilances. 
Some of thcfe ilrata have aftervvards been indurated, by which 
means they are turned into the above ilaty and limy clays 5 
and when they have beed mixed with a great quantity of 
•vegetables, and of the inflammable fubilance, they may in 
length of time be changed into pit-coal : but when they have 
been mixed with lefs ph'logiilon, and a great quantity of the 
vitriolic acid, tljey conilitiite the alum ores, &c. 
Others of thofe ilrata, which are not yet hardened, prove 
‘ ilill, by their being fet or divided with feme feparating veins 
of fand, that they ' hax'e been formed in the fame manner as 
the fettlings or fediments of damping mills, and may perhaps, 
through e'd ulceration in v;^atcr, or through age, have loft their 
fertility, iince they never are fo good to improve lands with, 
SIS thofe fira'a which are fuppbftd to be of a more recent for- 
■ utch as L d, 
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