The Age of the Earth. 
347 
the Mountains, and the more minute study of this region 
will doubtless enable us to trace antecedent and super- 
imposed rivers. 
The occurrence of copper in some of the shales in the 
lower beds of the Hawkesbury-Wianamatta is a subject 
worthy of further study. 
These are merely a few suggestions placod here to 
show what important questions are open to investigation 
to anyone who has mastered the first principles of the 
1 % 
science. 
APPENDIX C. 
T he Age of the Earth. 
Geologists rarely take years as units to measure time. 
With the public generally, it is just the opposite. When 
speaking of some geological fact, all at once one hears the 
question: “How long ago?” If people, for instance, become 
interested on learning that the Pennant Hills quarry is an 
ancient point of volcanic eruption, wo are immediately 
asked : “ How many years ago since all this happened ?” 
Strange as it may appear, the professional geologist seldom 
endeavours to frame an answer to these questions. In the 
study of geology one imperceptibly abandons the idea of 
accepting years as units of geological time. Quite recently, 
however, a goologist of high professional standing (Mr. 
J. G. Goodchild) has interested himself in the question. It 
is not possible hero to give even an outline of the data on 
which he bases his conclusions; but, as they are arrived at 
evidently with great care and a wide knowledge of the 
subject, it may be well to give his figures in tabular 
form : — • 
L See note on page 304 in reference to Professor Liversidge’s estimate of gold 
in the Uawkeabury Sandstones. 
