310 
Geology of Sydney. 
about. Darwin, as we have already stated, supposed 
the valleys were due to subsidence. Other observers 
thought that ocean currents cut out some of the 
depressions while the sandstone was actually forming. 
Popular theories appeal to earthquakes and the 
paroxysmal effect of internal fires. The geologist, 
while admitting the possibility of such causes to 
do the work, is satisfied that in running water we 
have an agent quite equal to the work — only givo 
it time enough. Someone characterised geologists 
as amiable (!) enthusiasts, who are happy if you give 
them plenty of what other men least value, namely, 
past time. For all that, as the science of geology 
becomes more studied, geologists become more insati- 
able for time. To repeat the words of Sir Archibald 
Geikie : — “ There is almost no amount of waste and 
erosion of the solid framework of the land which 
may not be brought about in time by the combined 
influence of springs, frost, rain, and rivers.” 
But, perhaps it will bring the matter more home 
to us to take a glance at some of the work done by 
running water in the world around us to-day. Every 
text-book for students of geology deals with the 
subject more or less fully. But for the general 
reader the best epitome of the more striking facts 
is that made by the Rev. H. N. Hutchinson, in his 
book “The Story of the Hills ”: — 
“The transporting powers of rivers are truly 
prodigious. Looking at a stream or river after heavy 
rain, we see its waters heavily laden with mud and 
