Synopsis. 
319 
drainage channels, till, after a vast lapse of time, they 
were shaped into the valleys as we now see them.” 1 
Synopsis of the Origin of the Mountains. 
1 The a ire of a mountain is estimated from the 
geological period in which it was finally lifted from 
beneath the sea. This, of course, does not apply to 
volcanic mountains, but only to mountains of sedi- 
mentary material deposited in the sea, or under some- 
what similar conditions in fresh water. 
2. In Silurian times, a wide stretch of ocean 
covered the region now occupied by the Blue 
Mountains. 
3. The folding of the Silurian sediments probably 
produced the first dry land. Between the deposition 
of the Silurian sediments and the beginning of the 
Devonian, a long period elapsed, during which the 
Silurian rocks were lifted from beneath the sea, 
folded, and then denuded in part. This is expressed 
by saying that there is an unconformability between. 
4. During the Devonian period there was a con- 
siderable area of dry land clothed with vegetation. 
These Devonian rocks were formed, some in fresh 
water and some under marine conditions. An uncon- 
formability also exists between the Devonian and the 
overlying Carboniferous. 
1 From an article contributed to the Railway Guide (Edition 1886), by the late 
Mr. Charles Wilkinson, Government Geologist. 
