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minerals but the findings from just over half were problematic. He
arrived at a date for the Silurian/Ordovician of 430 million years and
for the Devonian of 370 million years (Table
13.2
).
Table 13.2 Changing views of Arthur Holmes' Geological Timescale 1911
to 1960, compared with the 2004 timescale published by the
International Commission on Stratigraphy. The dates refer to the date of
the beginning of the geological units in millions of years, except where
indicated by
a
where the date of the end of the unit is tabulated instead.
The dates derived fromhelium are marked
b
. The 1947 figures are those of
his 'B' listing. Where Holmes gave a range of dates the greatest figure has
been listed.
1911
1915
1935
1947
1960
2004
Pleistocene
-
1.0
-
1
1
1.8
Pliocene
-
2.5
-
12
11
5.3
38
b
Miocene
-
6.3
26
25
23.0
8.4
b
Oligocene
-
-
38
40
33.9
30.8
ab
37
b
Eocene
-
58
60
55.8
Paleocene
-
-
-
-
70
65.5
60
a
Cretaceous
-
-
127
135
145.5
128
a
Jurassic
-
-
152
180
199.6
170
b
Triassic
-
-
182
225
251.0
42.7
b
Permian
-
205
203
270
299.0
320
a
196
a
Carboniferous
340
255
350
359.2
278
a
Devonian
370
380
313
400
416.0
Silurian
430
-
-
350
440
443.7
380
a
Ordovician
-
-
430
500
488.3
455
a
Cambrian
-
-
510
600
542.0
Precambrian
1,640
-
-
-
-
-
307
b
Upper Precambrian
-
600
-
-
-
Middle Precambrian
-
1,200
-
-
-
-
Lower Precambrian
-
1,500
-
-
-
-
