GR translation: lined beyond the thorn fences

[Mike Jing]

P322.17-26   Some of the more rational men of medicine attributed the
Herero birth decline to a deficiency of Vitamin E in the diet—others to
poor chances of fertilization given the peculiarly long and narrow uterus
of the Herero female. But underneath all this reasonable talk, this
scientific speculating, no white Afrikaner could quite put down the way it
felt. . . . Something sinister was moving out in the veld: he was beginning
to look at their faces, especially those of the women, lined beyond the
thorn fences, and he knew beyond logical proof: there was a tribal mind at
work out here, and it had chosen to commit suicide. . . . Puzzling.

What does "lined beyond the thorn fences" mean here?
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://waste.org/pipermail/pynchon-l/attachments/20130521/03bfa2d0/attachment.html>