THE HAWKESBURY SANDSTONE. 55 
Shoalhaven on the south, includes nearly the whole of its north and 
south extension. A similar line north and south between Sofala and 
Goulburn would be outside all its western boundaries, with one 
small exception near Sofala. These boundaries and the actual 
extent and thickness of the formation, can only be considered as 
approximate until an actual survey can be made. The geological 
map of the Rev. W. B. Clarke is only a sketch, in which in the 
course of time great modifications will have to be made. Thus, 
for instance, the same formation is found at Dubbo and along many 
places on the western plains, often of large extent, which are not 
indicated on the map. The Dubbo sandstone quarries have many 
plant remains, in which large and beautiful specimens of Thinn- 
feldia odontopteroides appear not to be scarce. There are also faint 
impressions of a leaf like G@lossopteris with mid-rib and oblique 
venation too faint for determination. 
Geological position.—In the whole of the area thus describe 
the formation lies horizontally upon rocks of different age. Some- 
times it is upon the coal measures, or again upon Devonian or 
Silurian rocks. It is overlaid in many places by the ‘Wiana- 
matta beds, and by basaltic, or at any rate volcanic products. But 
ion of upheaval. ‘here are, however, at 
the first Zigzag very many signs of a downcast or fault. There the 
beds are for a very short distance highly inclined against the range, 
having the appearance of an immense landslip from the failure or 
ete of the ground. The rock which is inclined appears to 
presents upon the map, one is struck by the great difference ~— 
anite 
tae generally meridional lines. The Silurian and Devonian forms 
e substratum of the eastern portion of the con- 
e, of which more subsequently. 
