308 
Geology of Sydney 
away — I received a kind of new revelation, so utterly 
above and beyond all my previous conceptions was the 
impression which the sight of this landscape now 
conveyed. The ridge of Pradolle is a narrow promon- 
tory of granite, extending eastward from the main 
granitic chain, and cut down on either side, but more 
especially to the south, by a deep ravine. It is capped 
with a cake of columnar basalt, which of course was 
once in a melted state, and, like all lava streams, rolled 
along the ground, ever seeking its lowest levels. A 
first glance is enough to convince us that this basaltic 
cake is a mere fragment, that its eastern and southern 
edges have been largely cut away, and that it once 
extended southward across what is now the deep gorge 
of Villar. Since the eruption of the basalt, therefore, 
the whole of this gorge has been excavated. But what 
agent could have worked so mighty a change ? We 
bethink us, perhaps, of the sea, and picture the breakers 
working their way steadily inland through the softer 
granite. But this supposition is untenable, for it can 
be shown on good grounds that, since the volcanic 
eruption of this district began, the country has never 
been below the sea. It is with a feeling almost of 
reluctance that we are compelled to admit, in default of 
any other possible explanation, that the erosion of the 
valley has been the work of the stream that seems to 
run in a mere rut at the foot of the slopes. How truly 
astonishing must be the working of such an agent, and 
how immeasurably far into the past does the contem- 
plation of such an operation carry us I . . Looking 
