166 Report on the Geological Survey of Connecticut. 
proceeding from the decomposition of granite, covering several acres. 
It forms an excellent material for small furnaces, and for lining an- 
thracite stoves ; the fire-bricks made from it are nearly equal to those 
of Stourbridge, England, and cost about two-thirds as much. Porce- 
lain clay is found also in Sherman, Kent, Cornwall, Granby, &c._ 
The feldspar quarry, below Middletown, affords inexhaustible and 
excellent materials for the manufacture of porcelain. Seven hun- 
dred tons were delivered at Middletown last year, of which 600 tons 
were shipped to Liverpool, and 100 to the porcelain manufactory 
at Jersey City. 
Siliceous sand of excellent quality for the manufacture of glass, 
is found in Middlebury. 
Fire-Stones.—Quartzy gray wackes, micaceous gneiss, mica-slate, 
and steatitic or asbestus-rocks, are often employed as fire-stones. 
Quartz rock and micaceous quartz rock are used for the same pur- 
pose. A rock of the latter kind used at Stafford “is arranged in 
Jamine of such thinness, that it requires at least fifty repetitions of 
them to form an inch. Each layer is completely coated with an 
almost unbroken film of white-mica. The rock cleaves with the 
utmost facility, and perfectly strait. The layers of quartz, more- 
over, are made up of slightly cohering, transparent grains, in conse- 
quence of which structure the rock is a very weak one, and may be 
broken with a slight force even in slabs of considerable thickness, 
and it may be cut and dressed on the edges with much more facility 
than the softest sandstone. It occurs at the quarry in strata nearly 
vertical ; and is shaped into blocks two feet square on the broadest 
face, by sixteen inches thick. In this condition it sells for sixteen, 
dollars per ton. The demand for the stone at. present is sufficient 
to afford constant employment to two quarrymen. The blocks sim- 
ply require to be so arranged in furnaces as to have their edges per- 
pendicular to the surface of melted metal. Some of these fire-stones 
at the furnace in Stafford, after they had been subjected to this use, 
were observed to have undergone a semi-fusion only, even where 
they had been exposed to the most intense heat. The silica on the 
exterior of each siliceous lamina had apparently been adequate to 
the saturation of the earthy bases contained in the mica, Jeaving the ° 
centre unaffected ; while the glass produced, had on the whole been 
sufficient to convert the stone from a friable, into a closely aggluti- 
nated mass. ss. Those fragments and masses of the rock not adapted. 
to use in 1 to sand aienaplcaed to some extent 
