200 W. R. BROWNE. 
The rock is a typical biotite granite and it exhibits con- 
siderable variation both in grain and in the proportions of 
ferro-magnesian minerals present. ‘This variation is of the 
usual type, that is with decreasing basicity and coarser 
grain inwards from the margin of the intrusion; this is well 
exhibited as one proceeds from the margin of the mass 
towards Berridale. A slight but distinct gneissic foliation, 
apparently primary, was noticed at one place, but the 
extent of this phenomenon was not traced. Basic segre-. 
gations are fairly numerous, and a number of aplitic dykes 
intersect the granite; some of these were entirely of the 
ordinary granular type, while others exhibited occasional 
graphic fabric, and others again had miarolitic cavities 
filled with tourmaline. 
On Arable Station just on the north-eastern border of 
the granite occurs a dyke of a dark grey porphyritic rock, 
without megascopic quartz, and of rather indefinite mega- 
scopic characters. In thin section the rock is seen to be 
of lamprophyric type. 
At every place where the edge of the granite was 
encountered a selvage of quartzite of varying width was 
found, while large quartz dykes were, as might be expected, 
very common. The quartzite border was noticed on the 
Adaminaby Road, on the Berridale Road and south of it, 
on Arable Station, and at Geygedzerick Hill. Contact 
effects were not specially looked for, but this constant 
occurrence along the irregular granite border suggests 
that the quartzite represents a complete replacement of 
the original sedimentary rocks by silica from the granitic 
magma for some distance from the actual contact. Another 
contact phenomenon has been already alluded to, namely, 
the production of chiastolite in the intruded slates. 
Myalla Road syenite.—Vive miles along the Myalla road 
south from Cooma, there is an isolated outcrop of syenite 
