January 6, 192 1] 



NATURE 



6.5 



breaking up of the husk, so that the endosperm falls 

 out in a clean condition. The endosperm is the most 

 digestible part of the grain and yields the best white 

 flour. Before the war only abput 68 per cent, of the 

 weight of grain was recovered as white flour, while 

 the remainder passed into various offals. During the 

 war the extraction of flour from wheat rose to more 

 than 90 per cent. ; this brought into use certain valu- 

 able food elements which, however, are not suited to 



ill constitutions. 

 Prior to the war only one-fifth of the wheat we 



onsumcd was home-grown; the rest came from North 



iiid South .America. Russia, India, and .Vustralia. 

 Some of these supplies are now cut off, and although 

 \merica has considerably increased her wheat acr&. 



Lie, the world's supply is still perilously short. 

 I or the ne.xt year the supplies are safe enough, but 



'10 permanent position is by no means assured, 

 i nless more land is put under wheat a bad crop in 



ne or two of the exporting countries would create a 

 -' rious world shortage, so that as a national insur- 

 ance we must grow more wheat. We can extend 

 our acreage, and we can increase our production on 

 the existing wheat-land, but in both cases better skill 

 and more knowledge are required. The country, then, 

 must be ready to encourage the attainment of know- 

 ledgi^, for ■■ on knowledge hangs our assurance of a 

 progressive food-supply in the future." 



The Origin of Primary Ore Deposits.* 



'PHE author commences at the period when the 



^ outer silicate shell of the earth was molten. 



i he primeval magma is regarded as having been 



lactically homogeneous and containing about 60 per 



' i-nt. of combined silicates. .'Ml water was then in 



'lie atmosphere, giving a pressure more than 300 times 



■> great as at present. .As temperature fell, water and 



\ygen were absorbetl ; crust-formation, foundering, 



id resorption went on for a long period, producing 



flat temperature gradient in the liquid. Viscositv 



\i'ntually rendered further foundering impossible; the 



[ ust became permanent, granite developed, and below 



the segregated basaltic magma long remained 



ijuid. .At this stage the isostatic balance was ad- 



isted. Ore-minerals in large quantity were given 



■f at the surface of the granite; these were denudeil 



ul dispersed in sediments and solution. This, with 



iter absorption by intruded basic magma, is assumed 



' have been instrumental in causing the present 



ratir distribution of primary ores. .All so-called 



iter in magmas is held to exist in combination as 



■ vl with silica not in solution as a gas. 



Tiiatic difTerentiation is reganled as having been 



aixd by the agcncv of silicic acid— silicon combined 



itii hvdroxyl — which extracts potash alumino-silicate 



■ iiducing a solution liehtrr than, and immiscible 

 ith, a melt of basic felspars and ferro-magnesian 



minerals. It is bclieve<l that in this wav the first 

 great split of primary magma into the world-wide 

 granitic and basaltic tvpes was brought about. Evi- 

 dence reganling the existence of silicic arid in mag- 

 mnfic liquids and elsewhere in Nature is addure<I. 

 The ultimate result of the action of water on rork 

 magmas is that silicates are completely removed and 

 n residue of ore-minerals such as magnetite, ilmenlfe, 

 and chromife left. 



Vein-fissurinc was brought about in and above 

 ^.^fhoIiths by the expansive force due to the increase 



■ solid specific volume of various elements. This 



I rcase is very considerable, exceeding in amount the 



Ah.ir.ct of. mn'r hy j. Morrow Camphall rmd btfor* lb* IttMiMlhm 

 MininfiiMt Metallu'ir nn Ortnhff >• igjo. 



NO. 2671. vor . rofil 



contraction on solidification of the granite, and con- 

 tinues throughout the whole of ttie crystallisation 

 period. The effect of this force appears in waves as 

 tissures in successive series. These developed very 

 rapidly, were instantly filled with magmatic mother- 

 liquor, and were quickly sealed by the deposit of solids 

 therefrom. 



Quartz is almost always present in veins along 

 with ore-minerals, and silica often occurs in solution 

 in thermal springs, especially such as carry gold, 

 arsenic, antimony, and mercury. For these and other 

 reasons it is regarded as probable that primary ore- 

 minerals passing up from magmas to veins do so 

 in silicic acid solution, and possibly in combination. 

 The deposition of these ores is usually caused bv loss 

 of heat and reduction of pressure. It is believed that 

 there are definite, but narrow, limits of temperature 

 between which each ore-mineral develops. These cor 

 respond to the temperatures in the strata at the 

 bottom and the top of the ore at the time of deposi- 

 tion. One persisting for a vertical depth of 2000 ft. 

 would, therefore, indicate normally a temperature 

 range of 20° C. 



The pneumatolytic theory of the origin of the high- 

 temperature ores is rejected because the phenomena 

 of their occurrence are quite inconsistent with what 

 would result if these metals hjd been given off as 

 gast's by magmas. The boiling points of tungsten 

 fluoride (19° C.) and tin fluoride (705° C.) are so far 

 apart that it would be impossible for wolfram and 

 cassiterite to have developed in contact with one 

 another, as thev frequently do. .Accessorv minerals 

 such as fluorite and tourmaline lose the genetic 

 significance usually attached to them owing to the 

 fact that they are not invariably present with tin 

 and tungsten ores, and are frequently associated with 

 a variety of other ores which are adiriittedlv of hvdro- 

 thermal origin. 



_ In introducing the paper the author directed atten- 

 tion to the probable importance of variations of 

 pressure in ore solution and deposition. .Separation 

 from simple solution would involve deposition of ore 

 .-"long the whole upward course of the solvent. This 

 does not take place, the end being usually abrupt in 

 an upvyard direction. The phenomena in Nature seem 

 to indicate that reduced pressure causes dissociation 

 and, at some point, the total removal of ore from 

 solution. Hifh temperatures and pressures are not 

 entirely correlative, and. since thev usually accom- 

 panv one another in Nature, it is' possible that as 

 regards ore-deposition we may in the past have been 

 confusing the two. 



University and Educational Intelligence. 



BiKMiM.iiAM.— I'he Tebbutt lectures on administra- 

 tion will be giwn during the coming term as follows : 

 "The Ontral Departments of Government and their 

 Relation to Local .Administration," by Prof. W. G. S. 

 .Adams; "Municipal .\dministration," bv Mr. .Arthur 

 Collins (treasurer of the City of Birmingham); 

 "Educational .Administration," by .Sir Graham Bal- 

 four; and "Business Administration," bv Mr. Gil- 

 bert C. N'yie (managing director of .Avery's, Ltd.). The 

 k'ctures will be open to the public. 



.Sir Wii.i.tAM BRtiNYATR has been anpointed Vice- 

 rhancellor of the I'niversitv of Hong Kong in succes- 

 sion to Sir Charles Eliot. 



It is stated in .Scicru-r of December t that an 

 anonvmnus gift of joo.ooo dollars has been made to 

 the fund which is being raised by thr Ainericnn Fn- 



