[ 432 ] 
to a Slag, or half vitrified Subftance 3 whereas the 
fame Heat, had it been Ivory or Bone, would have 
reduced it to a white Affi like Bone- Allies 5 for I cx- 
pofed it to fuch a Fire as vitrified the Tile that co- 
ver'd it. Its Hardnefs and Confidence to an En- 
gravers Tool feems to be the fame as common white 
Marble: Its Colour is not mended by Heat, but it 
grows brittle when red hot. 
This Specimen, now {hewn to the Society, was about 
12 Inches long, 5 Inches broad, and in fome Places 
near 2~ Inches thick,* rough on the under Side, as 
though broken off from the Rock it had been af- 
fixed to 3 and the upper Side was compofed of 
fmooth polifhed Knobs, in Form like to the botryoid 
Iron Ore. 
Sir Hans Sloane , in his noble Mufeum , has feve- 
ral Specimens of thefe oriental Turquoifes ,, all bo- 
* tryoid ; efpecially a Mafs from China, about three 
Inches long, two broad, and near an Inch thick : All 
which feem to be Copper Ores : And he has likewife 
Samples of Turquoifes horn Spain, and the South of 
France 3 which are all Email, and feem really to be 
Pieces of Ivory tinged with Copper. 
XVIII* A 'Defcription of a curious Echinites $ 
by Mr . Henry Baker, F. R. S. 
Head Feb. 26 **\ yFR. Baker takes the liberty of fliew- 
174 7 JLVjL in S Society & very extraordinary 
Echinites , the like to which he has never feen in 
any Mufeum , or found defcribed by any Author. 
For the Echinitse ufually met with, are made up 
cither of Chalk are Flint, or fome ftony, chalky, or 
7 fparry 
