This northern portion had been visited by Dr. Wallin; the other
two-thirds of the march lay, I believe, over untrodden ground. We
brought back details concerning the three great parallel Wadys;
the Salma, the Damah, that "Arabian Arcadia," and the
'Aslah-Aznab. We dug into, and made drawings and plans of, the
two principal ruined cities, Shuwak and Shaghab, which probably
combined to form the classical ; and of the two less
important sites, El-Khandaki and Umm Amil.

The roads of this region, and indeed of all Midian, are those of
Iceland without her bogs and snows: for riding considerations we
may divide them into four kinds:--

1. Wady--the Fiumara or Nullah; called by travellers
"winter-brook" and "dry river-bed." It is a channel without
water, formed, probably, by secular cooling and contraction of
the earth's surface, like the fissures which became true streams
in the tropics, and in the higher temperate zones. Its geological
age would be the same as the depressions occupied by the ocean
and the "massive" eruptions forming the mountain-skeleton of the
globe. Both the climate and the vegetation of Midian must have
changed immensely if these huge features, many of them five miles
broad, were ever full of water. In modern days, after the
heaviest rains, a thin thread meanders down a wilderness of bed.

The Wady-formation shows great regularity. Near the mouth its
loose sands are comfortable to camels and distressing to man and
mule. The gravel of the higher section is good riding; the upper
part is often made impassable by large stones and overfalls of
rock; and the head is a mere couloir. Flaked clay or mud show the