530 PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 
Loses in bath 9 * 259 per cent. of water. 
The occurrence in unaltered calcite leads to the conclusion that this must 
be an unaltered mineral. 
Increment of Water; decrement of Lime and partially of other Bases, but no 
decrement of Silica; hence an apparent increment of Magnesia. 
Incipient passage into Serpentine. 
Hydrous A sbestus.—Picrolite. 
24, 25. Alteration products showing this change are to be found in several 
places in the Shetlands. 
The lime and part of the iron first go, possibly by the direct action of car- 
bonic acid. 
At Doo’s Geo in Balta veins of a picrolitic substance are to be found; 
there is not in these in themselves any appearance of change; they are quite 
unweathered-looking, quite fresh, and to all appearance undergoing no altera- 
tion except in this, that the comparison of different specimens shows a gradual 
fading of the characteristic appearances of the one mineral, and a gradual 
assumption of the features of the other; and secondly, that in the specimens in 
which the latter is well marked, there is generally more or less fibrous calcite 
lodging between the filaments of the mineral. 
As a general description of these, they may be said to occur in dark green, 
finely fibrous masses of a greasy lustre and unctuous feeling; but it would be 
difficult to pronounce whether they were asbestus or picrolite. 
A specimen, presenting the extremes of each appearance, was analysed. 
The second specimen was more lustrous, more serpentinous, and somewhat less 
fibrous. Specific gravity of first, 2-693; of second, 2° 634. 

First. Second. 
On 1°3 grm. On 1 ‘302 grm. 
Silica, 2 : ~ pOrtgs 50° 076 
Alumina, . ; oo EOS 1: 876 
Ferrous Oxide, . 1 A893 6: 087 
Manganous Oxide, é 007 - 23 
Lime, . ; : i SUOT 86 
Magnesia, . 2 s* 29226 31 +566 
Soda, . : : : vas “341 
Water, A ; So tour) 9-302 
100: 228 100-338 
Insoluble silica of first, 4 - 636 per cent. 

