116 
G-eology of Sydney. 
conservative times. We laughed when poor old 
Colonel Greenwood published his quaint book entitled 
( Rain and Rivers/ wherein he showed that it was the 
earth’s atmosphere, and not the sea, which did all the 
wearing-and-tearing work. But geologists don’t think 
so now — and Colonel Greenwood is dead \” 
So far we have been speaking of how the sand- 
stones and shales were deposited. It is quite another 
question to discuss where the material was brought 
from. On this point our knowledge is not very com- 
plete. The making of the Hawkesbury Sandstones 
means the denudation and wearing down of an equal 
amount of country elsewhere. It would take a fair- 
sized mountain range to give the stones, so to speak, 
required to build up this formation. As far as 
geologists are aware, this high land stood away to tho 
south-west, and it was the rivers flowing from that 
direction that brought down the sediments, as mud, 
sand, and shingle, to make the sandstones and shales. 
These were afterwards re-distributed and spread out in 
layers in a sea so shallow that portions could become 
dry land, support a vegetation, and contain the lagoons 
in which the shales were deposited. 
Origin of the Ironstone Beds. 
Iron in some form or other is one of the most 
widely diffused of the metals. All plants and soils 
contain iron. Clays and rocks, with very few excep- 
tions, are coloured by iron compounds. “ Iron is 
