The sandstone hills are particularly interesting in that one finds a regular layer of coral on their summits, which shews that they were once nearly level with the sea, and are in fact coral reefs which have been elevated to heights of from 100 to 1000 feet. In some of those hills to which I have had access the corals on the summit are wonderfully well preserved, and by this fact, and that the species are indistinguishable from those now living in the sea, prove the elevation of the hills to have been geologically recent. Further, the larger coral colonies are at once seen to be still in the position in which they grew, not tilted or overthrown in any way. This is not the case with the older rocks on which they lie, the strata of which are frequently twisted and broken, and this is particularly noticeable sometimes in the case of the layer of gypsum which is often found between the coral and the sandstone (Fig. 89 on page 144). The hills are not marked on any map, indeed no survey has yet been made hereabouts. My account is therefore incomplete, but this does not invalidate the conclusions drawn. From seaward these hills are very easily distinguished from the jagged hills of archean rock, the true boundary of the Rift Valley, by their flat tops and the light yellow colour of their cliffs, and also by their generally being nearer the sea even than the great mounds of gravel which sometimes form the foot-hills of the mountain range. Passing from south to north the first range is met with a few miles north of Mersa[68] Durûr, as a chain of low butts rising from the alluvial plain a few miles inland. These become higher and more continuous as one passes northwards, culminating in two considerable hills, of about the same height and area of base, the northern of which is marked on the charts, where it is called Table Mountain, and given a height of 1000 feet. At about five miles inland from Dongonab are a couple of small hills standing alone, but a little farther north lying inland from the middle of the North Basin of Dongonab Bay is a considerable range, extending towards the hills about Khor Shinab, Hamama, &c., from which it is separated by an interval of only a few miles. The Abu Hamâma[69] range (which I so name from its most prominent though not highest peak, a landmark for sailors) extends from about the inner branches of Khor Shinab to some distance beyond Khor Abu Hamâma, lying much nearer the sea than do the others. Its height is estimated by a government surveyor at from 500 to 700 feet. (Map, p. 126.)