20O 



NATURE 



{July II, 1872 



ployed. A number of tables give some interesting details 

 relative to the number of miners, the machinery in use, 

 and its value, from which may be gathered some idea of 

 the extent and importance of the several gold fields in 

 the colony. Of these fields, that of Ballarat appeals at 

 the head of the list, showing a total numbsr of miners 

 employed of 13,892, the approximate value of mining plant 

 being 516,825/.; 134.I square miles of auriferous ground 

 are actually worked upon, and 189 auriferous reefs have 

 been proved. In this district also occur the deepest 

 shafts, two of which reach the depths of 866 ft. and 900 ft. 

 respectively. The price of Ballarat gold varies from 

 3/. 13^-. 6(/. to 4/. 2J-. bd. per ounce, the latter appearing to 

 be the highest price obtained for any gold in the colony. 

 In this mining district 78,502 toas locwl. of quartz were 

 crushed during the last quarter of the year, yielding 5 dwt. 

 19'42 gr. of gold per ton ; the average yield in the difTerent 

 gold fields being very variable. But in considering the 

 relative importance of each district, we are reminded by 

 Mr. Brough Smyth, the Secretary for Mines, that the table 

 relating to machinery should be examined and compared, 

 from which it appears that it is not always the mines that 

 show the greatest yield of gold which give the largest re- 

 turn to proprietors. An interesting feature in these reports 

 is the description by Dr. F. von Mueller (Director of the 

 Botanic Garden of .Melbourne) of certain new vegetable 

 fossils which are met with from time to time in the deep 

 auriferous drifts of older Pliocene age. These consist of 

 the fruits of plants which, according to Dr. Mueller re- 

 joiced in a milder climate, and displayed forms of tropical 

 grandeur now foreign to the spot. Five genera are de- 

 scribed and illustrated with beautiful lithograms. Of these, 

 among fossil genera Pliytnatocaiyoii comes nearest to the 

 extinct Cupanoidcs, Tn'carpcllifc's, and IVctlu-j-clIia of the 

 London Clay. Another genus, Tri'inatocaryoii, bears no 

 very close alliance with any genus among living or fossil 

 plants. The remaining genera are Rhytidothcca, with some 

 affinities to Chloroxylon and Ftindiisici, Plcsiocapparis, 

 the real affinity of which is doubtful, and Celyphina, 

 which appears to belong to the order of Proteacea;. We 

 are glad to learn that many other fossil remains have 

 been secured, and are now under examination by Dr. 

 Mueller. For the collection of these fossils paUcontolo- 

 gists are indebted to the enlightened zeal of Mr. John 

 Lynch, mining surveyor and registrar. When one looks 

 over the long list of surveyors and registrars employed by 

 the Colonial Government in gathering statistics, we can 

 only hope that some, if not all, of these gentlemen will 

 follow Mr. Lynch's example, and thus be the means of in- 

 creasing our knowledge of the " old world " of Australia. 



J. G. 



LETTERS TO THE EDITOR 



[ TIic Editor does not hold himself responsible for opinions expressed 

 by his correspondents. No notice is taken of anonymous 

 cotnmunicalions. ] 



The Rigidity of the Earth and the Liquidity of Lavas 



I WAS glad to see the powerful argument in favour of the 

 solidity of the earth which Sir William Thomson has deduced 

 fiom its great rigidity, republished in Nature of January iS, 

 since, though never attacked, it has been ignored by those wlio 

 hold a contrary view. In a lecture before the Royal Institution 

 in May 1867, I appealed to it in support of the notion which 1 

 have long maintained of a globe solidified from the centre ; and 

 I remember that for that and for other heresies in my lecture I 

 ^\^^s sharply attacked in the (Jcoloi^icdl J/a^azinc, and in turn de- 

 fended myself as best I might in the same magazine for February 

 1 868. I there said that " the conclusions of Hopkins from the 

 phenomena of precession and nutation, the investigations of 

 Archdeacon Pratt on the crushing effect of immense mountain 

 masses like the Himalaya, and the deductions of Sir WiUiam 

 Thomson fronj the plienomena of the tides, showing the great 



rigidity of the earth, are so many concurrent evidences that our 

 planet, if not actually solid to the centre, has a crust far thicker 

 tlian can be accounted for by the theory of a liquid globe, covered 

 only with a crust resulting from superficial cooling." This dis- 

 cussion of the subject at that time seems to have had the effect of 

 bringing to the front the defenders of the latter tlieo.'y, which, 

 in tlie popular mind at least, has a mythological rather than a 

 scientific foundation. It was, therefore, well th-.t Sir William 

 Thomson should repeat his argument;. 



Mr. Fisher has in this connectiop, in Nature for January 25, 

 referred to the distribution of fluid ignited matter within the 

 earth, a nd to the relation of volcanoes to great lines of elevation, 

 which would seem to show that the local distribution of such 

 matter may be connected with these lines. He says, "I have 

 suggested that this fluidity may arise from a diminished pressure 

 beneath mountain ranges, owing to their mass being pardy sup- 

 ported by tlie lateral thrust which has upraised them," and adds, 

 "If any of your correspondents can propose another explanation 

 of tliis remarkable coincidence compatible with the supposition 

 of a rigid globe it would be interesting to know it." 



My present object in writing is to call attention to the ex- 

 plrnation proposed by me in the Gioloi^'ica/ A/ii^a:inc (ot Febriis.\:y 

 1S70, conceiving, with Archdeacon Pratt, that the condition of 

 things beneath a great mountain mass is one of increased rather 

 than of diminislied pressure. I tliere said, " Pressure, which in llie 

 first case, that of simple fusion of anhydrous materials, prevents 

 liquefaction by preventing expansion, in the second case (that of 

 igneo-aqueous fusion, or liquefaction at higli temperatures, by the 

 aid of a small portion of water, as maintamed by Scrope, 

 Scheerer, and Elie de Beaumont) on the contrary, favours lique- 

 faction by promoting the solution of the water-impregnated 

 mass." As Sorby has shown, a conversion of mechanical into 

 chemical force appears in the increase of solubility under pressure. 

 In other words, pressure prevents fusion, when, as in most in- 

 stances, it is a process of expansion ; but favours solution, which 

 is, with few exceptions, a process of contraction. 



" Now since I place the se.at of volcanic action in a region 

 where solution, rather than simple fusion, is the cause of liquidity, 

 I am led to consider pressure as one of the efficient causes of the 

 liquefaction of rocks, and to regard its diminution as leading to 

 solidification." (See .also Amer. Jour. Science, ii., b 27). 



Montreal, June 21 T. Stekry HtJNT 



Fouling of the Nile 



There is an account — of which I have unfortunately lost the 

 reference — of the Nile becoming crimson and putrid, and its fish 

 being killed, during the historic period, seemingly by microsco- 

 pic alga;. If any learned contributor could tell me where I can 

 find this lact recorded, and could give me any details of similar 

 phenomena, he would do me an especial kindness. 



Chester, July 8 C. Kingslev 



Volcanoes of Central France 

 After carefully reading through the two extr.acts from Sido- 

 nius and Avitus contained in your number of May 30, my 

 impression was that notwithstanding some manifest improbabili- 

 ties, the conclusion was inevitable that earthquakes and other 

 volcanic phenomena had actually been witnessed at Vienne. 

 However, after examining all the facts of tlie case, a theory has 

 occurred to me by which both accounts may be consistently ex- 

 plained without any such phenomena having occurred there at 

 all. It would only remain to be shown that my supposed facts 

 are not contradicted by evidence actually on record. 



First, as to the persons : — The whole matter centres in 

 the great Gallic family of .Vvitus, belonging to Auvergne. 

 The most distinguished member of this famdy was Marcus 

 MiVcilius Avitus, a person of so much importance that in the 

 year 455 he became limperor, but so little fortunate that in Octo- 

 ber 456 he was conquered and driven from the throne. He was 

 allowed to become Bishop of Piacenza, but fearing for his life, re- 

 turned to Auvergne and took refuge in the Church of St. Julian. * 

 We find shortly afterwards two members of this family in 

 possession of the See of \'ienne, father and son, in succession, 

 and the latter was the author of our Homily. 



It seems, tlierefore, highly prob.able that the bishopric was 

 in the gift of the family, or in some way dependent on il. 

 In the year 463 we first find St. Mamertus in possession of tlie 



* According to Gibbon he died on the way ; the one cert.iin fact is that 

 he W.1S buried there. 



