REMARKABLE BOULDERS IN THE HAWKESBURY ROCKS. 107 
subject to rapid and changing currents. This sea was bounded o 
the west by the mountains which extend in a northerly direction 
from the Shoalhaven River to the head of the Goulburn River : it 
is in the rocks near the ancient shore liné that we should more 
especially expect to find ice-grooved pebbles, but none have yet 
been discovered. Its northern margin, owing to great denudation, 
stag so readily be determined, but it probably did not extend _ 
of the Hunter River ; and towards the on its extension 1s 
lost beneath the waters of the South Pacific oc 
e Hawkesbury Rocks are intersected Wes numerous sivdege 
joints, the principal of which strike about N. 15°—20° E., 
15°—20° W., with others at right et or nearly so, to ahaa, 
thus dividing the rocks into cubical masses. Intrusive dykes of 
trap occur in 1 several laces, and near these the sandstone some- 
times exhibits a well defined columnar structure. 
here remark that the sandstones and conglomerates — 
in which these conglomerates occur, and both Mr. Daintree and 
Mr. A. R. ©. Selw wyn, F.R.S., then Government Geologist, in their 
published reports, have ces their belief that glacial trans- 
Port had been concerned in the deposition of these rocks. 
