Geology Reference
In-Depth Information
the Whin Sill and the Cleveland Dyke, the control rocks were
believed to be, respectively, Late Carboniferous and Early
Tertiary, but clearly they were not. These significant geological
errors facilitated the acceptance of wildly inaccurate radio-
metric ages being assigned to these geological periods.
But in 1929 Holmes was not aware of the poor geological
constraints on the control rocks. As far as he was concerned,
both of Paneth's helium results were only 10 million years
younger than the uranium-lead determined ages for those
geological periods. So strong was the desire to find a successful
dating technique, he convinced himself that although the
helium results were
'slightly low'
, they concurred
'quite
satisfactorily with the scanty results based on lead ages'
.
Despite the historical problems with helium, Holmes could not
suppress his excitement:
'there is now available a practical
means . . . of building up a geological time-scale which,
checked by a few reliable lead-ratios here and there, should
become far more detailed than could ever be realised by
means of the lead method alone.'
At long last his dream of constructing a geological time scale
really seemed to be within the bounds of possibility.
