196 WwW. R. BROWNE. 
River the rest of the sequence is well shown. One passes 
in succession over grits, carbonaceous shales and quartzitic 
sandstones interstratified with shales in bands up to a foot 
in thickness. These are vertical at first but towards the 
river they have a westerly dip which decreases to 56°. 
Rhynchonella in great abundance, Strophomena, and (?) 
Tryplasma have been found in the grits and carbonaceous 
shales. The fossils are a good deal compressed, and their 
species are indeterminate. 
(d) Post-SILURIAN BUT PRE-TERTIARY.—To these rather 
wide limits are referred three apparently independent 
occurrences of igneous rocks, the quartz-porphyries, the 
Berridale granite, and the Myalla Road syenite. 
Quartz-porphyries.—This is a general term employed to 
denote a series of intrusions with many differences both 
textural and mineralogical, but evidently of common origin. 
They outcrop along roughly meridional lines, and so far 
have not been found west of a north and south line through 
Cooma, but intruded among the slates and other sedimentary 
rocks to the east and north-east of the town. Southward 
they disappear under the Tertiary basalt, to the north they 
have been traced as far as Bredbo, 20 miles from Cooma, 
where their extent is very great. They have played a 
considerable part in determining the contours of the present 
land surface, for, as one goes east from Cooma, it is observed 
that, generally speaking, the porphyries form a series of 
parallel low ridges, while the valleys in between have been 
cut out of the softer and less resistant slates. The por- 
phyries are perhaps best described as irregular dyke-like 
intrusions into the slates, although the outcrops attain a 
width of about half a mile in places. Their intrusive nature 
is abundantly proved by inclusions of the intruded slate, as 
wellas by the tapering terminations of the outcrops. Very 
little contact metamorphism is observable, barring a little 
local induration of the slates. 
