Geoscience Reference
In-Depth Information
Lower Carboniferous, and if they were to visit a locality in the middle
of this blue wash would know it to be underlain by fossiliferous lime-
stone. They know that the brown swathes distinguish the 'Old Red
Sandstone' of the Devonian from the pinks of the younger Triassic
'New Red Sandstone'. Equally, they comprehend that the areas of
scarlet represent the intrusive bodies of granite that welled up through
crustal rocks, and are now only seen at the surface through the erosion
of overlying layers of rock. If they were to visit one such mass of red-
coloured rock, they would know to bring their walking boots, a stout
stick and a good waterproof coat - nine times out of ten they would be
entering a mountainous or hilly region.
However, the conventional way of representing geology onmaps
does present difficulties, and they are frequently not easy for non-
geologists to interpret. Modern geological maps illustrate the chrono-
logical and not the lithological distribution patterns of rocks. Would
it not be better, particularly for those interested in fossil collecting or
those engaged in the extraction of stone aggregate for building or road
surfacing, to know where the most suitable rock types may be found?
Certainly it would. Perhaps the national geological surveys should
publish maps showing, for example, the distribution of granite in
red, sandstone in brown, siltstone in green, clay in yellow, coal in
black, and so on, until all the different lithological rock types were
distinguished by a characteristic colour. In reality, however, this
would prove almost impossible as there are many different lithologies
that could be represented. It could be done if the survey officers printed
themaps at very large scales, and used a palate of two hundred colours,
but then each map might resemble an impressionist painting, and the
information that it was supposed to impart would be lost in the com-
plexity of colour.
By the 1900s the geological column as we now recognise it was gen-
erally accepted and important in that it provided a moderatelymemor-
able terminology that was recognised globally. Equally the column,
and the relative position of any of the geological subdivisions, could be
