WHITE : OATLAND COMPLEX OF IGNEOUS ROCKS. 113^ 
For a similar reason, and in view of its close identity with 
the more basic facies at Oatland the age of the smaller intrusion at 
Ballabunt is considered to be contemporaneous with the earliest 
intrusion at Oatland. 
DETAILED DESCRIPTION OF THE ROCKS. 
A series of thin rock-sections made from specimens taken in 
various directions revealed the fact that a gradation in character 
is fairly constant from the most acid to the most basic type. For 
convenience of description, however, the complex may be 
resolved into three t3rpes of rock, acid, intermediate and basic. 
Among other considerations, which will be apparent later, we hold 
the acid facies to be distinguished by the presence of orthoclase,. 
and the basic by the absence of original quartz. The most acid 
type is found in the centre of the boss, and there is a fairly con- 
stant increase of basic characteristics as one proceeds to the 
margin, although it is not possible to fully test this in every direc- 
tion, and the megascopic examination of the rocks in the field 
indicates an increasingly rapid assumption of basic character 
towards the periphery. 
1. ACID TYPE. 
(Plate VIII). 
The rocks in this section are mostly adameUites, monzonites 
and granodiorites. They are, however, all characterised by the 
presence of a considerable amount of quartz, w^ith idiomorphic 
plagioclase, varjdng quantity of orthoclase, chlorite pseudo- 
morphs after biotite and a little hornblende. In each case the 
characters of the minerals will be described in the order in which 
they appear in the specimens arranged in a series of decreasing 
acidity. 
Quartz. — This has been the last mineral to crystallise. It 
resembles that of the Foxdale granite in having the granitic habit, 
while that of Dhoon and the Crosby microgranite (an elvan of 
the Foxdale mass) is quite granular. It should be remarked, 
however, that one section shows it as granitic and locally granular, 
another as mostly granular, and a third as having some undulose 
extinction. This is probably due to a merely local movement at 
the time of consoUdation. The quartz has the habit of com- 
pletely surrounding the other minerals and occasionally encloses 
