GEOLOGY OF THE COOMA DISTRICT, N.S.W. 189 
length: the main vein in Cooma has been traced south for 
about a mile, and it is probably the same which outcrops 
along the east bank of Cooma Creek a mile or so north of 
the town. None of the other outcrops have been traced 
for more than 150 yards. 
The contacts with the invaded formations are as a rule 
quite sharp. In the case of the Cooma pegmatite this is 
very marked indeed; here a great number of veins intersect 
the amphibolite and the gneiss, and in each case the hound- 
aries are very definite. 
In a number of the veins or dykes there is evidence of 
crushing subsequent to intrusion. This chiefly affects the 
margins of the dykes and shows itself in jointing parallel 
to the walls, and in marginal granulation of the pegmatite, 
producing a coarse aplitic-looking and rather friable rock. 
Most of the dykes exhibit this to some extent, but a notable 
exception is the Cooma pegmatite, which remains quite 
massive, this being possibly due to its being in the heart 
of the Cooma gneiss and so more effectively protected from 
crushing than those dykes which are among the less 
resistant schists. A certain amount of ragged-looking 
white mica often developed in the cracks of the felspars 
may be secondary. 
The relative proportions of quartz and felspar in these 
pegmatites are very variable, quartz being sometimes very 
subordinate and at other times the predominant mineral. 
The dyke at ‘‘Kiaora”’ is characterized by a number of 
elongated outcrops of quartz up to 8 or 10 yards in length, 
bordered by felspar and graphic granite. 
Quartz veins.—By the decrease and vanishing of felspar 
we have veins of tourmaline greisen and of quartz with 
tourmaline. These probably represent the last phase of 
pneumatolytic action, and have an origin similar to that 
