P | 
1 ’ ny) 
~ 
192 Ww. R. BROWNE. 
rocks are assumed to be Ordovician, as by their strike they 
are somewhat to the east of the Geygedzerick Hill slates | 
mentioned below. 
Dense black slates outcrop between Cooma and Bunyan, 
and at Bunyan to a distance of 400 yards east of the Sydney 
Road. No fossils have so far been discovered in them, but 
their marked contrast with the Silurian slates farther to 
the east, and their lithological similarity to those west of 
Slack’s Creek, seem sufficiently striking to determine their 
age aS Ordovician. The exact eastern boundary of these 
slates is not known, its determination being rendered 
difficult by the quartz-porphyry intrusions, by cappings of 
basalt, and by the recent alluvials of Cooma and Middle 
Flat Oreeks. However there is a distinct difference in 
appearance between these slates and those outcropping 
further to the east which are definitely Silurian, so the 
Ordovician may be taken as having its eastern boundary 
approximately as given on the map. 
At Bunyan these slates have been locally silicified, or 
replaced by silica, with retention of their original cleavage 
and other characteristics. This I can only ascribe to the 
intrusion of the white gneiss: traversing across the strike 
one observes all gradations from evident gneiss to equally 
evident silicified slate; there is no distinct line of demar- 
cation between them. 
Although they are not included in the map, and are 
somewhat beyond the area dealt with, some mention must 
be made of the Ordovician slates of Geygedzerick Hill, 24+ 
miles N.H. of Berridale. Iam indebted in the first instance 
for information as to their existence to Mr. L. Grater, a 
science student at the University of Sydney, who kindly gave 
me.some specimens of the slates which he had picked up on 
the spot. The hill, or rather ridge, looks to be the end of 
a tongue of slates and quartzites almost surrounded by 
