348 
Geology of Sydney. 
Time in Years. 
For the Tertiary Period .. 
For the formation of the Chalk, Upper Greensand, 
Gault, and lower Greensand 
Pre -Cretaceous Unconformity in Britain ... 
Time required for the deposition of the Jurassic - 
Wealden Series ... 
Time represented by the Trias and Permian rocks 
Unconformity at the base of the lower New Red in 
Britain 
Duration of the Upper Carboniferous Period in 
Britain 
Time required for the formation of 2,500 feet of 
Carboniferous Limestone... 
Time represented by the Continental Devonian 
Limestones... 
Duration of the period represented by the Silurian 
rocks 
93.420.000 
31.400.000 
13.200.000 
59.400.000 
87.500.000 
45.000. 000 
31.815.000 
62.500.000 
125,000,000 
56.000. 000 
Chronological value of the Unconformity at the 
base of the above ... ... ... ... ... 12,000,000 
Time required for the accumulation of the upper 
Ordovician rocks .. ... ... ... ... 12,000,000 
For the Lower Ordovician rocks ... ... ... 33,000,000 
For the Upper and Middle Cambrian rocks ... 36,000,000 
For the Lower Cambrian rocks ... ... ... 6,000,000 
704,235,000 
The time required for the known geological series, or the time 
that has elapsed since life is known to have appeared on the 
earth, is estimated at 704,235,000 years. The age of the earth 
would, of course, be vastly greater. 
