
GEOLOGICAL SURVEYING 277 
some of the paper ruled into squares. These squares may 
represent inches, feet, or yards, and thus enable the observer 
to sketch on a correct scale any rock exposure which can be 
conveniently measured. Until some facility in drawing has 
been attained, it is best to use first a common lead-pencil, 
and afterwards to ink-in the lines. With practice, however, 
the observer may eventually be able to discard the pencil and 
to sketch directly with his pen. For clearness’ sake it is often 
advisable to colour a section. Coloured pencils may serve for 
this purpose, but in a note-book such colours are apt to get 
rubbed and smudged, and ordinary water-colours, therefore, 
are preferable. Those who have an artistic aptitude enjoy a 
great advantage, and can often do without the help of square- 
ruling—bringing out with a few deftly drawn lines on plain 
paper all the geological features that call for expression. They 
can fill their note-books also with sketches of scenery which 
may show at a glance how the configuration of the ground 
has been determined by the nature and structure of the 
rocks. If the observer have this gift, he would do well to 
cultivate it—for he may be sure that his descriptions of 
geological phenomena will gain enormously in clearness and 
value when they are accompanied by well-selected artistic 
illustrations. 
To others who have not been blessed with artistic talent, 
photography lends much assistance, and is therefore largely 
indulged in by field-observers—good portable cameras being 
readily obtainable. 
The Topographical Map.—Reliable topographical maps of 
most civilised countries can now be obtained. In our islands 
the maps issued by the Ordnance Survey cannot be surpassed 
for accuracy, and are just such as are desiderated by the 
geologist. These maps are on various scales—those on the 
scale of six inches and one inch to the mile respectively being 
most useful for geological purposes. The beginner will find 
the larger scale map the more satisfactory of the two, as it 
enables him to plot his observations in much greater detail 
than would be possible on the other. The shape of the 
ground is indicated by numerous contour lines (ze. lines of 
equal elevation), instead of by “hill-shading,” so that pencilled 
notes and lines are clearly seen, and the observer is usuall 

