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forms Rocks of Tophus along the Rive-hide, com- 
pofcd of Strata of fevcral Colours, according as the 
Water has been impregnated with different Matter, 
or perhaps from the Difference of Heat or Cold, or 
the Impreflions of the Air at the times of forming the 
Lamella . ?. This Tophus is hard, and receives a 
good Polifh, and of it they make Snuffboxes, Heads 
of Canes, and other Toys. Some Years ago, in 
digging to lay the Foundation of a Church, forty 
or fifty Paces higher up the Hill, they found vaft 
Quantities of this Tophus , which was in many Places 
fo decayed and rotten (refembling very foft Clay), 
that they were obliged to dig fcveral Fathoms deep, 
before they could find a folid Foundation. Here 
they threw out great Quantities of the Tifolithus , of 
the Kinds I fend you, which are compofed of the 
fame Matter as the Tophus , though of a very dif- 
ferent Conftru&ion : The Tophus being made up of 
Plains joined together, whereas the ‘ Tifolithi arc glo- 
bular, and compofed of fevcral fpherieal Shells. Some 
Globules are found above an Inch in Diameter, but 
more commonly about the Bignefs of white Peas, 
and decreafing gradually in Size till they become as 
fmall as fine Sand, and at laft common Tophus . 
The feveral Shells which compofe thefe Globules 
differ in Colour as the Lamella of the other Tophus 
do : But thefe Shells fcpaiate more cafily than the 
Lamella , and (hew that the Colour often confifls 
in one very thin Shell between two thicker ones. 
Such kind of Tophus , with Tifolithi , is found at 
other Places j but I have never yet met with any 
body who could give a fatisfa&ory Account of its 
Formation. Some think th zTiJblithi are Drops of 
Water 
