On 10 Feb, 19:57, Tom Anderson wrote:

And a question: why do there not appear to be any sleepers in the old
engraving?

Because it's mixed gauge track, standard 4' 8.5" standard and 7' 0.25"
Great Western Broad Gauge. The GWR originally laid their rails on
longitudinal baulks of timber, with timber transoms and metal tie-bars
at intervals to hold them to the correct gauge. This form of track
construction is sometimes still used; I saw it in Paddington Station a
few years ago, and it's also sometimes used on bridges, possibly to
reduce the weight.

There's a picture of the mixed gauge trackwork at Didcot at the bottom
of this page:

http://www.didcotrailwaycentre.org.u...ormation.shtml

You can clearly see the construction of the trackwork. I did some of
the work on this track, about twenty years ago now.