SOME GEOLOGICAL NOTES ON COUNTRY BEHIND JERVIS BAY. 309 
2. The Sassafras tableland and the Currockbilly Range 
form a dissected ‘horst’ or ‘block mountain.’ 
3. Faulting movements of Tertiary age probably account 
for the north and south trend of the creeks rising near 
Sassafras. The Ettrema approximately follows a paleeozoic 
fault line along which small movements may have taken 
place in Tertiary time. A line of weakness and severe 
jointing so formed has rendered the affected parts subject 
to easy attack by subeerial erosion. As soon as the under- 
lying paleeozoic rocks were reached the N. and 8. direction 
would become accentuated, the paleeozoic structure lines 
having that trend. In the EKttrema the creek at the mine 
has after cutting through the sandstone, followed a palzeo- 
zoic fault which has been impregnated with ore bodies. 
No doubt river captures, such as that described by Dr. 
W. G. Woolnough near Marulan have aided to bring about 
the peculiar direction and disposition of the streams. 
4, The occurrence of a glacial horizon in the Upper 
Marines of Ettrema Creek is suspected. 
od. Late Tertiary basalt eruptions are shown to have 
followed upon the formation of the Sassafras horst and to 
have been accompanied by local subsidences (as in the 
Endrick). 
6. The fault formation throughout the area belongs to 
two periods—the Carboniferous and the late Tertiary. In 
both cases the fissures run approximately north and south. 
7. The Devonian rocks occupy a basin:lyingbetween two . 
Strips of Silurian or Ordovician age, the one extending from 
Milton to Nelligen, the other from Nerriga to Braidwood. 
This Devonian trough was folded and elevated in the 
Carboniferous. 
8. The Devonian and late Permo-Carboniferous were 
periods of sedimentation. The Carboniferous witnessed 
