28 
Geology op Sydney. 
to be quite beneath their notice, and that all attempts 
at accurate calculations from such small data are quite 
inadmissible. What other science, however, has pros- 
pered by adopting such a creed? What physiologist 
would think of ignoring all the invaluable discoveries 
that have been made in his science with the microscope 
merely because the objects are minute? . . . With 
such striking examples before us, shall we physical 
geologists maintain that only rough and imperfect 
methods of research are applicable to our own science? 
Against such an opinion I certainly must protest; and 
I argue that there is no necessary connection between 
the size of an object and the value of a fact, and that, 
though the objects I have described are minute, the 
conclusions to be derived from the facts are great.” 1 
The study of a rock indoors can never be alto- 
gether satisfactory. We must, if possible, see the rock 
in the cutting, ravine, or cliff. We must learn its 
relation to surrounding rocks. Not until we have done 
this may we say that we are in possession of sufficient 
facts to gather together the history of that rock, by 
deductions based on these facts. 
The principle underlying all geological study is 
that this earth is subject to change. The crust of the 
earth is now subject to disturbance and dislocation. 
The interior of the earth is probably solid, with no 
doubt lakes of molten matter. Some authorities hold 
for a liquid interior. But the one thing beyond dis- 
1 Geol. Soc , Lond., 1858, p. 497. 
