498 PROFESSOR HEDDLE ON THE RHOMBOHEDRAL CARBONATES. 

Carbonate of lime, . : , : ; : 50026 
- of magnesia, : iy ; 3 39°108 
s ofiron, . : ; : : 6°7: 
$s of manganese, 3 : : , i 3°736 
Silica, ; : ; ; : one P 422, 
Insoluble, : ; : , ; 62 
100-41 
The four carbonates are here in the ratios— 
Cai’ Met’ fe Nn 
50 44 6 3 
The theoretical specific gravity of such a compound is 2-946. 
Pearl spar from Walls, Orkney.*—Occurs in a dark purple amygdaloid to 
the west of Sandsgio, filling druses which are lined with green earth. It 
frequently contains large white lamellar crystals of baryte imbedded in its 
substance ; sometimes crystals of translucent analcime line the sides of the 
druses, and very rarely brown “ Babel quartz.” Its cavities sometimes contain 
curved crystals ; its colour is pink; its specific gravity is 2°780; its crystals 
and cleavage too curved for measurement, 
Its analysis afforded— 

Insoluble (quartz), . : E : . , 16 
Carbonate of lime, . ; ‘ ; ; 2 62°4 
5 of magnesia, : P : : . 32°056 
5 Ohi WOM, : . , : : 1:74 
5 of manganese, ; i : 5 ; 4:276 
100-632 
The four carbonates are here present in the ratios— 
CaC MgG FeC Mn 
42 24. 1 24 
The theoretical specific gravity, 2°88. The association of baryte and analcime 
with both of these pearl spars is worthy of remark. 
Dolomite pseudomorphous after calcite-—Occurs in druses in trap tuff north 
of the Rock and Spindle, at Kinkell, St Andrews. Besides the mineral, the 
ifs druses contain salmon-coloured rock crystal, blue baryte, 
and nail-head calcite. The Dolomite is pseudo after the 
scalenohedron 7 (“ dog-tooth ” scalenohedron) in general; 
the portion analysed was however pseudo after the more 
complex form depicted. 

* Incorrectly entered as Ankerite in Grea and Lerrsom’s “ British Minerals,” on the writer’s 
authority, 

