Geology Reference
In-Depth Information
reached the top of a convecting cell beneath a continent it would
travel horizontally for some distance before cooling and
descending again. As it travelled horizontally it would produce
a force that was su~cient to drag the continents sideways, and
so the continents were very slowly pulled apart allowing the sub-
stratum to rise up and take their place in the ocean floor.
Leading geologists, particularly the Americans, were
exasperated by these ideas, as this letter from William Bowie
illustrates:
Holmes brings out a new thought which is even more impossible than
Wegener's. That is that the submerged ridge through the Atlantic Ocean
is the place at which North and South America separated from Europe
and Africa, the latter two continents drifting eastward and the Americas
drifting westward. I do not see how the same force, operating to send one
INEN
Region of
Tension
A
nding
arly S
Islan
Sw
B
asaltic
rises
nding
(Sta
g
Continental drift.
These diagrams illustrate what Holmes cautiously called
'
a purely
hypothetical mechanism for “engineering” continental drift'
. He
described how in A the sub-crustal currents are in the early part of
the convection cycle, while in B
'the currents have become
sufficiently vigorous to drag the two halves of the original
continent apart, with consequent mountain building in front where
the currents are descending, and ocean floor development on the
site of the gap, where the currents are ascending'
.
