June 15, 1916] 



NATURE 



329 



I 



GEOLOGY OF SOUTH-WEST AFRICA. 



T is not often that a geological memoir appears 

 in such inspiring circumstances as that issued 

 v the Mines Department of the Union of South 

 Africa on "The Geolog>- and Mineral Industry of 

 South-west Africa " (Pretoria, 1916, price 7s. 6d.). 

 -Mr. P. A. Wagner writes with an eye tor geographic 

 I atures and for plant-associations, and his photo- 

 -,raphic illustrations, such as that of the Okavango 

 Iviver, or that of the noble barchans in the sand- 

 desert, convey vivid information in regard to the new 

 territory- of the Union. Here and there in his ad- 

 mirably written text a war that has recently taken 

 l^lace is casually mentioned ; otherwise the transference 

 of this rich and developing mineral territory from one 

 Government to another could only be guessed by the 

 quiet excision of " German " from its official name. 

 An exact Dutch translation follows the English text, 

 and the titles beneath the pictures are given in both 

 languages. In a few minutes we find ourselves at 

 home with the simple phraseology of our African com- 

 rades, and the memoir will form an excellent lesson- 

 book for mining men travelling out to '"Walvis 

 Bay." 



Mr. Wagner's description of the geology, accom- 

 panied by a remarkable, if provisional, coloured map, 

 shows how the features familiar through the Cape 

 Province stretch bevond the Kalahari region to the 

 coast. Certain shales in the Karroo formation appear, 

 however, to be marine in South-west Africa, and 

 Lx)wer Miocene strata occur in detached areas south 

 of Liideritz Bay. The composite gneisses of the basal 

 complex are fineh' illustrated from Diamantberg. In 

 ■ the author's review of the ven,- varied mineral pros- 

 pects we are glad to note that the Union Government 

 has arranged for the protection of guano-producing 

 birds. The output of minerals so far has been prac- 

 tically confined to the very prosperous diamond-fields 

 of the Liideritz coast, and the copper ores of the 

 Grootfontein district in the north-east. 



Mr. Wagner directs attention to the great explosion 

 which formed the ring of Geitsi Gubib, north of 

 Berseba (Bathsheba). This ring has been recently 

 described by Mr. A. W. Rogers (Trans. Roy. Soc. 

 S. Africa, vol. v., p. 247), who shows that, contrary to 

 Dr. Schenck's opinion, volcanic rocks are not to be 

 found in its materials. The "breccias" and tuffs are 

 formed mainly from shattered sediments, together with 

 some fragments of deep-seated holocrystalltne rocks. 

 The central "crater" is merely the result of denuda- 

 tion acting on a softer tuff within a wall of more 

 resisting but equally fragmental matter. The whole 

 jnountain is a volcanic neck about a mile and a half 

 in diameter, choked bv its products of explosion. 



G. A. J. C. 



ANTARCTIC HYDROGRAPHY. 



MANY of the scientific results of the Scotia Ant- 

 arctic Expedition (1902-04) of Dr. W. S. Bruce 

 have now appeared, but want of funds has seriously 

 delayed the publication of the valuable observations. 

 The Royal Society of Edinburgh, which has done a 

 great deal to further the publication, has issued in 

 its Transactions (vol. li., 4, pp. 71-170) a lengthy 

 memoir on the temperatures, specific gravities, and 

 salinities of the Weddell Sea and of the North and 

 South Atlantic Ocean by W. S. Bruce, A. King, and 

 D. W. Wilton. The surface observations were taken 

 daily by Mr. Wilton from the beginning to the end 

 of the expedition, except during the wintering of the 

 Scotia at the South Orlcneys, and extend from the 



NO. 2433, VOL. 97] 



North Atlantic to the Weddell Sea via the Falkland 

 Islands, and home vid Gough Island and Cape Town 

 to St. Helena and the Azores. In Antarctic waters 

 observations were generally taken every four hours, 

 and sometimes oftener. In addition, many readings 

 were taken at depths down to 3000 fathoms. 



Dr. Bruce recounts the minute care exercised in 

 taking the observations, which deal with nearly six 

 hundred samples. The densities were determined by 

 hydrometers lent by Mr. J. Y. Buchanan. Deep 

 samples were obtained by the Buchanan-Richard 

 water-bottle. Occasionally the Pettersson-Nansen in- 

 sulated water-bottle with the direct-reading Richter 

 thermometer was used, but for polar work this has 

 its drawbacks, quite apart from its excessive cost and 

 the liability of loss in bad weadier. The fine screws 

 are difficult to manipulate with cold fingers, and it is 

 questionable whether the insulation is trustworthy at 

 low air temperatures. In one case the contents were 

 frozen solid when the bottle came on deck. On the 

 other hand, the Buchanan-Richard bottle is cheap, 

 easily manipulated, does not jam by freezing, and is 

 trustworthy at any depths. Nor is it probable that 

 errors are frequent or large due to variations in the 

 point at which the mercury breaks in the reversing 

 thermometer. In the case of every sample, in addi- 

 tion to the data relating to collection, those in relation 

 to the determination of its density are given. The 

 densit}'^ is given (i) at the temperature of the experi- 

 ment, (2) at 1556° C, (3) at the temperature of the 

 sea at the time the sample was taken. This last gives 

 the actual density of the water in situ. Some of these 

 calculations are the work of Mr. A. King, and all 

 the others have been checked by him. Exigencies of 

 space and e.vpense have prevented a full discussion of 

 the results and the addition of charts, but, neverttie- 

 le^s, the memoir constitutes the finest contribution ever 

 made to Antarctic hydrography. 



PORTLAND CEMENT. 



PORTLAND cement has in recent years come into 

 such extensive use for a variety of purposes that 

 particulars concerning it should interest a wide circle 

 of readers. In vol. lix. (part iii., January, 1916J of the 

 Transactions of the Institution of Engineers and Ship- 

 builders in Scotland, appears a paper by Mr. B. J. 

 Day on the manufacture, properties, and testing of 

 Portland cement, with a special description of a cement 

 works erected by the author at Aberthaw, Glamorgan- 

 shire. This article forms the basis of the following 

 short descriptive account ; and by Mr. Day's courteous 

 permission we are able to use two of the illustrations 

 which accompany his paper. 



The difference between limes and cements should 

 be clearly understood. Common lime, made by burn- 

 ing pure limestone (composed essentially of calcium 

 carbonate), slakes in water, but has no hydraulic 

 properties (does not harden or set under water). 

 Hydraulic lime, made by burning at a low temperature 

 impure limestones or limestone mixed with clay, slakes 

 on adding water, and has hydraulic properties. Port- 

 land cement is made by burning at a high temperature 

 — to incipient fusion of the material — a definite mix- 

 ture of limestone with clay or shale, and finely grind- 

 ing the resulting clinker. The powder so obtained has 

 strong hydraulic properties. It is important to distin- 

 guish Portland cement from Roman cement and cer- 

 tain other natural cements, and slag cements, all of 

 which are inferior in strength and less constant ia 

 composition. 



The original Portland cement, patented in 1824 by 

 Joseph Aspdin, of Leeds, was so called because after 



