\ 
= 
Dh 
is 
AGE OF THE 
aR 2) 
as dR 
80 ea 
c oF 
S§ S'S 
ee Lo 
83 sz 
LS ¢ §3 
u 4 
Zz w 
~ 
EARTH—HOLMES 
229 
Unconformity 
between AandB 
Figure 1.—Diagrammatic section to illustrate the rocks and structures of a series of orogenic 
belts (A, B, C, and D), such as make up the continental crust of the earth. 
greatly exaggerated.) 
cycle, and those of the Lake District 
and most of Scotland and Wales and 
Norway belong to the next earlier one. 
From beneath the North West High- 
lands of Scotland and the mountains 
of Scandinavia the rocks of even older 
cycles appear (pl. 2, fig. 1). So, going 
further afield than Hutton, we can 
travel back through a long series of 
these contorted records of earth his- 
tory. But however far we penetrate 
into the past we still, like Hutton, find 
“no vestige of a beginning.’ How 
this comes about can readily be 
grasped by reference to figure 1. In 
every continent the oldest known rocks 
are found to be metamorphosed sedi- 
mentary types which gradually merge 
into completely reorganized rocks 
such as granite. The granite, how- 
ever, instead of being older than the 
rocks in which it is emplaced, is actu- 
ally younger, since it crystallized in its 
present form during or after the folding 
of the pile of sediments with which it 
is associated. Everywhere the oldest 
visible rocks pass sideways or down- 
wards into walls and foundations that 
are younger than themselves. But 
since the oldest visible rocks are of 
sedimentary origin, they must have 
been derived from rocks of still greater 
age; from rocks that were reincarnated 
as granite long ago and of which no 
other recognizable trace can now be 
found. Hutton’s experience covered 
only a small proportion of the earth 
history now known to us, and he was 
therefore recording no more than the 
sober truth when he declared he could 
find ‘‘no vestige of a beginning.” 
Unfortunately this conclusion was in- 
(Vertical scale 
terpreted by most of Hutton’s con- 
temporaries to mean that, according 
to him, the earth never had a begin- 
ning, and so was never created. Thus, 
far from being welcomed, Hutton’s 
discoveries were generally regarded 
with righteous horror as being con- 
trary to the Scriptures, while he him- 
self was accused of having ‘“‘deposed 
the Almighty Creator of the Universe 
from his Office.”” But Hutton was not 
without a circle of loyal friends and 
admirers in Edinburgh; the modest 
fame in which he died 150 years ago 
soon developed into a_ world-wide 
appreciation of his genius. 
Hutton himself, in the absence of 
guiding data, made no attempt to 
estimate the rates of geological proc- 
esses. Many of his successors, how- 
ever, exhilarated by their newly found 
freedom, became unduly reckless in 
their extravagant demands for time. 
In 1859, for example, Darwin esti- 
mated from the supposed rate of chalk 
erosion in Kent that the time required 
for the denudation of the Weald and 
the recession of the bordering escarp- 
ments of the North and South Downs 
to their present positions was probably 
about 300 million years. We now 
know that this estimate was at least 
five times too long; but Jukes, com- 
menting on it at the time, thought it 
quite as likely that the period required 
might have been a hundred times as 
long. Evidently 30,000 million years 
was not considered absurdly excessive 
for a small fraction of geological time. 
Kelvin, one of the great pioneers of 
geophysics, then entered the field with 
a dramatic counterblast against such 
