On Feb 24, 3:52 pm, Paul Terry wrote:
In message id, Dr J R
Stockton writes

I've misplaced a better answer; but the unused hole is a bit over one
train-width to the north, and a few yards to the east, of the working
one. The ends are easily seen.

Ah, got it!

When built, both tracks of the Kingston loop buried

burrowed?

under the main line
at Elm Road, and then ran in parallel with (but independently of) the
main line (i.e. on what are the southern pair of the four tracks). So
the mysterious hole was for the Kingston Loop up-line

The up line presumably being Kingston to Wimbledon (worth confirming,
as of course both routes out of Kingston go to London).
Did the rearrangement happen when the Wimbledon flyover was built (or
v.v.) ?

In message m,
writes

The up line presumably being Kingston to Wimbledon

Yes.

Did the rearrangement happen when the Wimbledon flyover was built

No, the Wimbledon flyover came much later (1936, I think).

From the late 19th-century until 1936 the lines were paired by direction
all the way to Waterloo, causing enormous problems because the slow
services and fast services had to cross on the level at Waterloo station
throat to get to the right set of platforms.

The Wimbledon flyover solved this problem by getting the fast (up and
down) services onto one adjacent pair of tracks and the slow (up and
down) services onto the other adjacent pair without a crossing on the
level, in advance of the terminus. A long way in advance, of course, but
I guess it was the most practical and cost-effective place to make the
switch in pairing.
--
Paul Terry