522 Reviews—Geits. Gubib, an old Volcano. 
strata newer than the Carboniferous; since, as is set forth in the 
preface, measured thicknesses of rocks older than this period are of 
little or no value; while as for the Carboniferous system itself, © 
records are so numerous that there is little need to repeat them. 
The country is divided into counties, which are described either 
singly, or two or three together, where geographical or geological 
conditions make this necessary. ach area by itself forms the subject 
of a chapter, beginning with a map showing, as far as possible, all 
the places mentioned in the text. A general description of the 
rocks follows, beginning with the newest and going down to the 
oldest, in which the most important variations in thickness of each 
formation are discussed. Finally, a tabulated list of the records of 
the principal deep borings is added at the end of the chapter. The 
book affords an admirable and simple method of obtaining much 
information which could only be obtained hitherto by prolonged 
search through libraries.—W. H. W. 
III.—Gaurrst Gupin: an Oxp Vorcano. By A. W. Rogers. Trans- 
actions of the Royal Society of South Africa, vol. v, pt. iii, 
December, 1915. 
EITSI Gubib is a ring-shaped mountain, rising 5,200 feet above 
sea-level, and 1,800 feet above the plateau north of Keetmans- 
hoop in South-West Africa. The ring is from one mile to a mile 
and a quarter in diameter, and has a depression in the centre 
1,500 feet below the highest point of the ring, which is drained by 
a stream flowing through a gap in its south-east side. The mountain 
itself is composed of fine-grained clastic rocks dipping steeply inwards. 
The junction with the Fish River Sandstones is vertical, and can 
be seen in the valley of the stream; in the same place it can be seen 
that the sandstones also dip inwards at the junction. ‘The rocks 
themselves consist of breccias and tuffs; the breccias are formed of 
fine-grained sedimentary rocks, with some fragments related to the 
quartz gabbros, in a cement of quartz and dusty material. Fragments 
of orthoclase, plagioclase, and augite are found in them. The most 
notable features are the entire absence of true volcanic rocks and of 
large blocks, there being none above oneinchin diameter. ‘he silica 
cement seems to be harder and better developed round the outside of 
the mountain, and it is to this fact that it owes its ring-shape. 
This disposition of the cement is almost certainly due to the rising of 
waters charged with silica round the margin of the vent. No trace 
of the fragmental material which was thrown out on to the surrounding 
country now remains, and it is obvious that the original cone and 
surface have been worn away, leaving the hardened plug standing 
above the present plateau. The depression in the centre is therefore 
not acrater, though it occupies the same relative position. Dr. Rogers 
suggests two possible origins for the mountain; these are, first, that 
it was an ordinary explosive crater, and second, that the clastic rocks 
have been let down by a circular fault. Of these the first is more 
probable, as there is little brecciation along the line of junction; and 
it is also borne out by the existence of sattelite pipes with igneous 
