
= 
PROFESSOR HEDDLE ON THE RHOMBOHEDRAL CARBONATES. 497 
25 grains afforded— 
Insoluble (quartz), . : ; ‘ 204 

Carbonate of lime, . : : : : : 55:08 
Ps of magnesia, , : : : : 37°092 
5 ofiron, . ‘ , : : ; 5°716 
re of manganese, : 5 ; : : 1368 
Alumina, i ; : , : ; : 116 
, 99:576 
The ratios here are— 
CaC MgC FeC MnC 
55 42 5 1 
The theoretical specific gravity is 2°912; the theoretical angle, 106° 10’. 
Dolomite from Largybaun, Cantyre—The mineral here was found in the 
cliffs a little to the south of the Largybaun caves, which are situated about half 
way between the Mull of Cantyre lighthouse and the house of Ballygroggan. 
It is associated with limonite ; occurs of a fawn-yellow colour; and is in large 
cleavable masses ; these are somewhat decomposed in spots into a bright red 
ochre. From its colour it was taken for chalybite. Its specific gravity is 
2°824 ; its cleavage angle, 106° 30’. 
25 grains afforded— 

Insoluble (quartz), . : : : eke : 048 
Carbonate of lime, . ; : : 2 ; 55:80 
7 of magnesia, : : ; : : 36296 
35 ofiron, . : , : : : 6°612 
“agg of manganese, A : ; : : 1:264 
100-02 
The four carbonates are here in the ratios— 
CaC MgC FeC Mn 
56 41 6 1 
The theoretical specific gravity of such a compound is 2°92; and its theoretic 
angle, 106° 9’. 
Dolomites from igneous rocks. 
“Pearl spar” from the round sea stack north of the “Rock and Spindle,” 
near St Andrews. This occurs filling druses in a thick vein which cuts the 
tuffa; the vein has occasional cavities lined with crystals, which are sometimes 
studded with “ nail-head ” (rhombohedron g) calcite. This pearl spar contains 
large white lamellar crystals of baryte imbedded in it. Analcime is found 
closely adjacent, imbedded in a vein of brown calcite. Colour, pink ; specific 
gravity, 2°782 ; crystals and cleavages too curved for measurement. 
VOL, XXVII. PART IV. 6Q 
