in the case of operations carried out at private expense, thanks 
to the cordial co-operation of many of the boring engineers, and 
to the ready response to requests for information, fairly complete 
bore records, which might otherwise have been lost, are filed in 
the archives of the Department. 
Much, however, yet remains to be done before a really 
complete set of the journals of private bores has been collected, 
for there is no legal obligation on the part of the public to lodge 
such data with the Government, even though the operations may 
have been carried out on what is really State property. Unless 
some steps are taken to acquire the information there is a pos- 
sibility that a vast amount of valuable geological data may be 
irretrievably lost. 
Petrology. 
In addition to the field work to which your attention has just 
been directed, microscopic enquiry now forms an important part 
of the operations of the Department, for there are very many 
practical problems requiring special investigation in connection 
with the rocks of the auriferous formations. 
The microscope has also to be employed in conjunction with 
the chemical balance, and both brought to bear on rocks, the 
relation of which to other rocks have been carefully investigated 
in the field. It may, perhaps, be of interest to you to indicate 
the mode in which the microscope is applied to the examination 
of minerals and rocks. 
Slices cut by one of the many forms of the lapidary’s wheels 
from the rocks or minerals are ground down smoothly until they 
are but a small fraction of an inch in thickness ; they are then 
mounted on glass by Canada Balsam. The effect is to make the 
great majority of the ordinary constituents of rocks translucent 
if not transparent. They are then examined under a specially 
constructed microscope fitted with Nicol’s prisms and other 
contrivances for optical tests. These refined optical tests often 
afford information leading to the discrimination of minerals 
where chemical analysis would not be available. When all the 
varieties of minerals occurring in a rock have been identified, 
one's work has only just begun, for its structure and history have 
to be investigated. 
The mounted rock slides are properly registered and kept in 
a separate cabinet ; a large number of slides have been accumulat- 
ed, the collection amounting to about 1,400, and are ready for 
immediate reference at any time. The results of this microscopic 
work are embodied in the various official reports. Perhaps one 
of the most important petrological reports is from the pen of 
Mr. J. A. Thomson, B.A., B.Sc., F.G.S., which will be found in 
Bulletin No. 33. This gentleman’s observations make by far the 
most noteworthy contribution to the petrology of the fundamental 
rocks of Western Australia which has yet been issued by the 
