The Work of the Geological Survey. 
151 
ores of the western counties and in developing the great South 
Wales coal-field. Yet the maps remain as they were originally 
published. The Geological Survey has of itself no power to under- 
take revision, and much as we would like to see all the mineral fields 
re-surveyed and brought up to date, we cannot go faster than Parlia- 
ment will sanction or the Treasury will authorise. Two years ago, 
in response to an important memorial from South Wales, we received 
instructions to commence the re-survey of that coal-field, and the 
work is now in active progress. I trust the day may not be distant 
when similar revisions will be made of the other mineral-fields 
which were surveyed many years ago on imperfect 1-inch maps. 
The re-surveys of the mineral districts can now be carried out 
on the 6-inch scale with a completeness and accuracy unattainable 
when the original surveys on the 1-inch scale were made. In some 
cases the maps of mining districts have been published on the 6-inch 
scale, but where the sale is likely to be small, instead of incurring 
the heavy expense of engraving the 6-inch sheets, we issue manu- 
script copies of these sheets at the cost of manual transcription. 
As an illustration of the kind of work undertaken by the Survey in 
the mining districts, I may refer to the Maps, Sections, and Memoir 
of the Yorkshire coal-field. There is no reason, save that of 
expense, why all the mining districts of the country should not be 
similarly treated. 
Though systematic re-surveys are not undertaken by the 
Survey without express sanction, it is customary to make minor 
corrections which from time to time may be required in the published 
maps. Those counties in the south and south-west of England of 
which the superficial deposits were not originally mapped are now 
undergoing revision for the “ Drift Survey,” and advantage is taken 
of the re-examination of the ground for the insertion of the surface- 
geology to make any needful alteration on the lines of the solid 
geology. 
II. Petrographical Work. 
In the earlier days of the Geological Survey each member of the 
staff determined for himself, by such tests as he could apply, the 
various rocks encountered by him in the field. Only in rare cases 
were chemical analyses made for him. The study of rocks had 
fallen into neglect in this country, being eclipsed by the greater at- 
traction of the study of fossils. The introduction of the microscope 
into geological investigation has, however, changed this apathy into 
active interest. It is now recognised that, apart from mere ques- 
tions of nomenclature, rocks contain materials for the solution 
of some of the most important problems in physical geology. 
Accordingly, microscopic inquiry has in recent years been 
organised as one of the branches of the Geological Survey, and now 
affords constant and material aid in the progress of the mapping. 
Chemical analyses are likewise made, so as to afford all available in- 
