328 Reviews—The Nitrate Shales of Egypt. 
6. During this period a process somewhat analogous to secondary 
enrichment occurs, resulting in the growth of larger diamonds at the 
expense of minute crystals. 
7. The economic diamond is therefore to be regarded as essentially 
a secondary mineral grown in situ in the kimberlite matrix. 
IV.—Tue Nirrare SHatzs or Keypt. By Dr. W. F. Home, Assoc. 
R. C. Sci., F.G.S., Director Geological Survey of Egypt. 
N Mémoires de l'Institut Egyptien (1915, vol. viii, pp. 145-69) 
Dr. W. F. Hume summarizes the work in connexion with the 
nitrate shales of Egypt. Generally they have yielded on analysis 
5 per cent or less of sodium nitrate. The difficulty in their 
commercial development has been caused by their variability in 
distribution. They are present at a definite horizon in the geological 
series, forming part of the uppermost Cretaceous strata (Esna Shales 
and Ashgrey Clays), and have been traced from Farafra Oasis to West 
Sinai. Their wide distribution at the same horizon suggests that they 
represent compounds formed or absorbed at the time of deposition of 
the shales; on the other hand, the presence of sodium nitrates being 
only marked near the surface suggests that they are either formed by 
some means now acting, such as nitrifying organisms working under 
moist conditions of the soil, or have been drawn to the surface by 
capillarity. 
V.—Geotocicat Survey or New ZEALAND. 
Burtetin No. 17, New Series, or tHE GeotocicaL Survey or New 
Zeatanp. By P. C. Morgan and J. A. Bartrum. pp. vui-+ 210, 
with 19 plates, 18 figures, 9 maps, and 6 geological sections. 
Wellington, 1915. 
f}\HE authors give an exhaustive account of the geology and 
mineral resources of the Buller-Mokihinui Subdivision, Westport 
Division, which district lies on the west coast of the South Island. 
The mining industries include gold-mining, mainly alluvial, which 
was at one time very prosperous, but is now almost extinct, coal- 
mining, and to a small extent rock-quarrying. ‘he supplies of 
coal, particularly the bituminous variety, in New Zealand are very 
limited, and will probably approach exhaustion in at the most one 
hundred and fifty years. The bituminous coal as yet known is 
contained almost wholly in the Greymouth and Westport Districts. 
The authors call attention to the loss of coal resulting from the 
methods of working it. The geological formations consist of two sets 
separated by a striking unconformity: the one is composed of highly 
folded grey wacke, argillite, hornfels, schist, gneiss, and intrusive acid 
igneous rocks, which were base-levelled in pre-Tertiary times, and on 
this peneplain was deposited the second set of strata, consisting of 
a succession of breccias, conglomerates, grits, sandstones, mudstones, 
and limestones, in places unconformably capped by Quaternary sands 
and gravels. The Bulletin is excellently illustrated. 
