114 WHITE : OATLAND COMPLEX OF IGNEOUS ROCKS. 
sub-angular fragments of its own species. Fluid pores arranged 
lineally or in strings increase in number and size from very few to 
very many. Some contain gas cavities. Staining with iron-ore 
is shown between some of the crystal faces. Inclusions become 
more and more numerous, comprising apatite, small flakes of 
muscovite probably derived from the orthoclase, zircon, epidote 
(sometimes as disconnected granules in parallel strings, perhaps 
derived from neighbouring hornblende), zoisite, some large 
crystals of iron-ore, and an unidentified mineral which appears 
in two specimens. This latter mineral is of irregular outline and 
colourless. It has no fluid pores ; against it the quartz with its 
crowd of fluid cavities is everywhere arrested, but it contains one 
or two negative octahedral crystals, probably of fluid. It is 
chatoyant by reflected light, is isotropic, and has a refractive 
index about equal to that of quartz, greater than felspar, and 
less than biotite. 
Measuring off the intercepts of the minerals by Rosiwal's 
method in the various sections, and calculating their gravimetric 
proportion in the rock, it was found that quartz decreases from 
37 per cent, to 18.4 per cent, in this acid facies. 
Orthoclase is always present, but in varying quantity. Its 
outline is usually irregular as in other Manx granites. 
Fig. 1. 
Fig. 2. 
