APPENDICES 383

small pieces at Jaub Anbak. These occurrences are probably
connected with the Miocene beds of these districts.

Limonite.—The e iron pan J so common in many sandy forma-
tions does not appear to be frequently found in the Eube al Khali.
Three specimens, supposed at first to represent rounded concre-
tions of ' iron pan,' were found on close examination to be stony
meteorites similar to the one found by Mr. Bertram Thomas at
Buwah in Sawahib. They are the subject of a special note.1

Limonite with a highly polished surface was collected near
Dhabba in 'Anna, and in the form of ' iron pan ' and ferruginous
tubular concretions appears on the surface near Dughm in the
Riyadh district.

4

2. STBATIGRAPHY AND PALAEONTOLOGY.
BY L. R. Cox, M.A.,

Department of Geology, British Museum.
(a). Tlie Jurassic Rocks of Jabal Tuwaiq.

Mr. Philby's previous journeys have shown that the Tuwaiq
plateau, whose western edge forms a continuous escarpment, 500
to 800 feet in height, from Wadi Dawasir in the south to beyond
Zilfi in the north—a distance of over 400 miles—is formed by
Jurassic rocks. Immediately to the west, in the plain, there are
extensive exposures of limestone of somewhat earlier age than
the rocks of the escarpment, but so far these have yielded no
fossils. Still farther west, as far as the igneous complex of western
and south-western Najd, the older rocks are masked by vast
spreads of gravel. A few fossils collected from three localities on
the Tuwaiq plateau (Bakkain to the north-west of Riyadh, and
'Ashaira and Hamar about half-way between Riyadh and Wadi
Dawasir) were described in 1921 by R. B. Newton,2 who considered
their age to be Sequanian or Kimmeridgian.

On his most recent journeys Mr. Philby has collected numerous
specimens from the Tuwaiq Jurassic, largely from richly fossil-
iferous exposures in the neighbourhood of the Haisiya pass, to
the N.W. of Riyadh, but also from the Sha'ib Markh district,
50 miles farther north, and, in the south, from Khashm Amur,
where the Wadi Dawasir cuts through the Tuwaiq escarpment.

The Haisiya fossils are preserved in a brittle light yellow marly
limestone and include ammonites, which enable their age to be
determined definitely as Upper Callovian. The following are
among the species from this locality.

J< Meteoric stones from Suwahib, Arabia,' by W. Campbell Smith,
Mineralogical Magazine, March, 1933, vol. 23.

* Ann. Mag. Nat. Hist.9 9th series, vol. viL, pp. 389-403.