130 WHITE : OATLAND COMPLEX OF IGNEOUS ROCKS. 
chemical composition closely agrees with that of the diorite from 
Netherley, Strathspey, also with the diorite from Benn au Thurian, 
except that in the latter the ratio between potash and soda is 
inverse. 
THE ROCK AT BALLABUNT. 
Two sections from this small intrusion were examined and 
the results showed that the rock presents close correspondences 
with that at Oatland, which occurs only two miles to the S.S.W., 
in a direction parallel to the structural axis of the island. 
Quartz has the granitic habit, as at Oatland, and is crowded 
with fluid cavities. 
Felspars have also the habit of those in the more acid rock 
at Oatland. They are extremely decomposed, apparently to 
white mica, and cases of twinning can rarely be detected. A 
few forms gave extinction angles of about 13 degrees. 
Biotite of green colour in pseudomorphs of chlorite enclose 
octahedra and irregular grains of titanomagnetite together with 
a few veins of epidote. 
Augite occurs in some quantity, now uralitised and of a very 
pale green colour. It is almost always twinned. Some sub- 
idiomorphic green hornblende and tangles of actinolite, the blades 
of which often cross at angles of 84 degrees, occur in the interior 
of the cr3'stals. The refraction of the actinolite is less than that 
of the surrounding hornblende. Some apatite is included. 
Hornblende of a dark green colour occurs on the borders of 
the augite and usually, but not always, optically continuous 
with it. A little compact green hornblende also occurs apparently 
not connected with the augite but frequenth' moulded on the 
biotite. The crystals are usually more compact than those at 
Oatland. 
Iron Ores. Ilmenite is the most abundant but scales of 
haematite occur in the augite and the green hornblende. 
