Geology Reference
In-Depth Information
improve upon. Thirteen years later when Holmes came to revise
the scale he was quite happy to acknowledge that it had outlived
its usefulness and joked that
'now I come to bury the B scale,
not to praise it'.
Both Arthur and Doris worked extremely hard, trying to build
up the geology department in Edinburgh to its former glory, but
perhaps inevitably this interesting and intellectually vigorous
couple once again attracted tremendous controversy. This time
it was about their work. For years Doris had been working on
granites, and the question that puzzled her most, and many
other workers in the field, was 'how had they originated?'. In
Britain we are familiar with granites in places like Dartmoor and
Cornwall, where granite tors stand out above the landscape.
These are in fact only the surface expression of a much more
massive body of granite that probably links all the tors together
underground and which may extend many miles down into the
crust of the Earth. In other parts of the world, the Himalayas for
example, the lateral extent of these massive bodies is exposed
at the surface and can be traced for hundreds of miles. They are
the roots of ancient mountain chains, now long gone, but in the
1940s little was understood about their origins.
Doris had a theory; she called it 'granitisation'. The model
proposed that fluids migrating upwards in the crust from with-
in the bowels of the Earth, 'a flux of emanations' as she called
it, soaked into the existing rocks adding new elements and
thereby turning the rock into a granite. One of the features of
this theory was the 'basic front', which formed as a halo around
the altered rock as the incoming fluids drove out dark elements
such as iron and magnesium. Norman Bowen, a Canadian geol-
ogist and leader of the opposing theory, that granites evolved
from basalts, described the basic front as a 'basic
a
¬ront' to
much popular acclaim! The two schools of thought became
