19 
passing through the “ Gap,” a break in the precipitous and rugged 
escarpment of Hawkesbury Sandstone, which here unconformably 
overlies the untilted Silurian rocks. The latter can be seen 
almost vertical along the river-bed road previously mentioned, 
with a general north and south strike, the junction of the Silurian 
and Hawkesbury rocks taking place a little below the escarpment. 
The plateau now reached, and of which Mounts Bulee and 
Sassafras only form portions, consists of a high tableland of 
Hawkesbury Sandstone, and possesses many features in common 
with the physical aspect of the district north of Port Jackson. 
The Bulee escarpment exhibits some grand examples of rock 
weathering, the particular form here taken being the castellated, 
producing large detached buttresses gradually decreasing upwards, 
and disintegrating in thin layers or laminas, like so many 
pancakes piled one on the other. 
Prom above Bulee Gap the road proceeds over the tableland, 
now rising, now descending, but never to any great extent, until 
the summit of Mt. Sassafras is insensibly reached. A short 
distance before Mr. Greg’s accommodation house comes into view, 
a marked change takes place in the appearance of the ground, 
which suddenly passes from the glistening sandy soil of the Hawkes- 
bury Sandstone to a rich red and brown loam, resulting from the 
decomposition of the basaltic rock of which the summit of the mount 
is composed, but when first struck the latter rock appears only as 
cappings to the low spurs of sandstone. The basalt is described 
by Mr. 0. S. Wilkinson as intrusive,* and I have been favoured 
by my colleague, Mr. W. Anderson, of the Geological Survey, 
with the following notes on' this rock from specimens collected by 
us. “ It is a dolerite consisting of triclinic felspar, augite, olivine, 
and magnetite, but none of the minerals showing much decom- 
position. The olivine contains many included crystals of 
magnetite, and neither it nor the augite show distinctly crystalline 
outlines, the latter occurring as large irregular shaped pieces, in 
which are embedded both felspar and olivine, showing that it 
was one of the latest minerals to crystallize out.” 
At the Gap our attention was called by Mr. C. II. Roberts to 
a large branch of fossil wood, which had been obtained in situ in 
the Hawkesbury Sandstone. It is silicified, microscopic sections 
failing to yield more definite details than the feet that the 
wood is probably coniferous. 
Mt. Sassafras is the highest point on the watershed between 
the heads of the Clyde River on the south, and the Ettrema and 
Danjcra Creeks, branches of the Yalwal Creek, a tributary of 
the Shoalhaven River, on the north. It is stated to be 3,125 
feet above sea level, and rises considerably higher than the 
tableland around it. 
* Ann. Report Dept. Mines, N. S. Wales, for 1885 (188G) p. 132. 
