WHITE : OATLAND COMPLEX OF IGNEOUS ROCKS. 121 
The hornblende in this part of the section closely resembled 
that in the intermediate and basic t3rpes in presenting two varieties, 
one with a pleochroism greenish-blue to pale yeUo wish -pink and 
-extinguishing usually at 22 degrees and 23 degrees ; the other 
with a pleochroism greenish-brown, brownish-green and pale 
straw. The latter is about three times as abundant as the former. 
The greenish-blue crystals are often sub-idiomorphic and con- 
tiguous to biotite. ActinoUtic needles with extinction up to 
"9 degrees sometimes radiated from the hornblende into the 
biotite. The browTiish-green variety in its larger patches con- 
tained some magnetite dust and suggested that it had been derived 
from augite or the brown hornblende usually included in it. 
ORDER OF CRYSTALLISATION IN THE ACID TYPE. 
The order in which the minerals commenced to form in the 
central or acid portion of the boss is the same in all the sections 
examined and is as follows : — 
1. Apatite and zircon. 
2. Iron ores. 
3. Biotite and hornblende. 
4. Orthoclase. 
5. Plagioclase. 
6. A little hornblende (in the less acid part only). 
7. Quartz. 
SUGGESTED AFFINITIES. 
The chemical composition of most of the specimens, based 
upon the quantitative mineral composition, suggests that the 
most acid type resembles the composition of the " potash- 
granite " from Lamome, Cornwall, and closely resembles that 
of the Skiddaw granite and the granite of the Moume Mountains, 
while it is not far removed from the potash-soda felsite from 
Waterford, the Oatland rock being deficient in alumina but 
having an excess of magnesia. 
The granodioritic tyipe mineralogically resembles the quartz 
diorite from Arran, described by Zirkel, and by TeaU, " Brit. 
Petr.," pp. 263-4. 
