Geology Reference
In-Depth Information
Following his physical breakdown in 1948, Arthur Holmes
returned from recuperating in Ireland in time to attend the Inter-
national Geological Congress, being held that year in London.
In his address from the chair he once again challenged current
thinking, this time by turning the accepted geology of Africa
upside down:
'The time has come to liberate Pre-Cambrian
geology from the tyranny of a telescoped classification'.
Geologists in the audience, such as Robert Shackleton, who was
also working on the Precambrian of Africa, remember to this
day a flash of revelation as Holmes re-drew the geological map
of Southern and Central Africa, based on a relatively small num-
ber of radiometric dates.
'No one could be more aware than I
am how few and . . . how unsatisfactory are most of the age
determinations already available. Nevertheless, poor and few
though they be, they are unlikely to place a group of rocks in
its wrong cycle and they serve to show what far-reaching con-
clusions can be drawn.'
Holmes made geologists sit up and
realise, probably for the first time, how important radiometric
dating was in revealing the relationship of one rock to another,
thereby illuminating the geological processes that had gone on
in the dim and distant past:
'Obviously, all previous correla-
tions not based on absolute dating have been no more than
“shots in the dark”, and if occasionally they scored a bull's eye
it was only by chance.'
Finally, he could not resist a parting
shot:
'When maps such as the one here presented are com-
pleted for all the major Pre-Cambrian areas . . . they will provide
a reliable criterion for testing the continental drift hypothesis.'
Such was the impact on the geological community of Holmes'
work on Precambrian geology that it ultimately resulted in major
government funding for the establishment of laboratories for
geological age determinations in Britain, France, and Belgium,
but they were not completed in time to be of value to him.
Holmes spent much of the remainder of his working life trying
to unravel the mysteries of the Precambrian, whose rocks rep-
resent eight-ninths of geological time.
