
PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 237 
1-3 grammes yielded— 
Silica, : * 824 
From Alumina, ° 047 

-881 = 67-789 
Alumina, . ; : 18° 764 
Ferric Oxide, . 1-428 
Manganous Oxide, . "076 
Lime, ; > *516 
Potash, . J ; TOT 
Soda, : ‘ : 10 : 492 
Water, : ; ERs) 
99-981 
Insoluble silica, 1° 362 p.c. Possible impurity, magnetite. 
From Serpentinous and Talcose Rocks. 
3. On the south shore of Colafirth Voe, in the mainland of Shetland, there 
is an assemblage of such rocks lying between the red aplite of Roeness and 
Colafirth hills and the mica slate of the east shure. Several varieties of ser 
pentine occur in close proximity with the aplite. These are all bedded, but 
thrown up at a high, almost a vertical angle. Three well-marked varieties,—a 
dark green,—“ potstone” like,—granular serpentine ; a light green, with blue 
dendritic markings ; and a verdigris green,—cannot be distinguished from three 
similar varieties which occur at Portsoy : there also they occur as tilted beds ; 
the strike is the same, and the order of succession from west to east identical. 
Dr Hiszert states that he found the breadth of two of the masses of serpen- 
tine to be 90 and 240 feet—the writer found the two principal masses at Port- 
soy to measure 80 and 240. 
HIssektT, in describing this spot, writes—“ On the south of Colafirth Voe, 
the particles of the gneiss are disposed into distinct strize of hornblende, quartz, 
felspar, or mica. At the same place, where there is one of the finest sections 
that is to be seen in Shetland, a beautiful rock succeeds, that is composed of 
nothing more than striz of quartz and hornblende.” Further on he adds— 
“Tn addition to these substances, beds of quartz from 3 to 7 feet broad occur, 
with some trifling quantity of a pure white limestone.” 
Hreserr’s use of the words particles and striw here is peculiar. By par- 
ticles I understand him to refer to the several constituents; by strize, as used by 
him the first time, I understand beds; as used the second time, I understand 
layers or bands. 
VOL. XXVIII. PART I. 3 Q 
