Align St 5, 1880] 



NATURE 



317 



seem to accord well with the statement above (July 31) that he 

 had only "just ascertained" the fact to his "great surprise." 

 —Ed.] 



Subterranean Kaolinisation 

 A YEAR ago Mr. John Arthur Phillip;, in criticising, before 

 the Geological Society, my theory of kaolinisation as a source of 

 superficial rock temperatures, made a point which is interesting 

 in its bearing upon the composition of derived or secondary 

 lithological products. He endeavoured to ascertain the number 

 of tons of felspathic rock that must be yearly kaolinised in order 

 to supply the quantity of alkalies known to be contained in the 

 mine waters of the Comstock silver lode in Nevada, and in doing 

 so he began with the supposition that iu the process of kaolinisa- 

 tion all of the alkali in the felspar goes into solution and is re- 

 moved. This assumption is undoubtedly incorrect, for even the 

 surface clays -which are deposited from running water, aud there- 

 fore must have been subjected to a maximum leaching, almost 

 invariably contain potassic and sodic salts, as any one may learn 

 by studying the subject of fireclays. 



But when the clay is formed by the alteration of rock at great 

 depths, beyond the line of ready drainage and in the presence of 

 a minimum quantity of water, the product is, or may be, quite 

 different from the clay of sedimentary deposition. It is in fact 

 merely the original rock hydrated, and from the example given 

 in the Comstock region the alteration product does not seem to 

 lose much, if any, of its original alkalies. This is demonstrated 

 by the analyses given in Mr. King's Report on the Fortieth 

 Parallel. AH the existing analyses of the clays in this region 

 were made on specimens obtained in the first thousand feet of 

 depth, and most of them were taken within 500 feet of the sur- 

 face. That is, they all come from the region of active drainage, the 

 oxidising and other effects of atmospheric action being well marked 

 in this lodedown to the depth of 600 feet. The meanof four analyses 

 of clays shows 4'72 of alkalies and 10 '86 of water, COo and P2O5. 

 One of the specimens has been very strongly altered, having lost 

 about 10 par cent of silica, while another seems to have gained 

 about half as much of the same constituent. As to the composi- 

 tion of the original rocks (propylite and andesite,) it is impossible 

 to be exact, for the alteration in the region has been so extensive 

 and thorough that all attempts to obtain an unaltered specimen 

 have failed. The least altered specimen of propylite from the 

 Virginia range of mountains in which this lode is found contains 

 5"oS per cent, of alkalies, with I '02 loss by ignition. Tlie most 

 altered specimen contained 5 '26 per cent, of alkalies, and 6'S5 

 loss by ignition. Andesite showed iu the least altered specimen 

 4'7 alkalies and 2"S loss ; in the most altered specimen 7"37 

 alkalies and 4'35 loss. It is impossible to compare the clays of 

 this district with unaltered rock from other localities, for the 

 reason that tlie composition of these eruptive rocks varies strongly, 

 especially in the percentage of alkalies. On the whole I think 

 that any one who will compare the tables of analysis given in 

 vols. i. and iii. of Mr. King's work will be convinced of the 

 truth of what I have asserted above — that subterranean kaolini- 

 sation is merely the hydration of a rock in place without other 

 serious alteration. The fact has importance in its relation to 

 the origin of some hydrated aluminous rocks. 



Mr. Phillips calculates that the average proportion of alkalies 

 in these rocks is 6'4 per cent., that 813 tons of alkalies are 

 removed yearly in the mine waters, and that "it consequently 

 follows" that the felspar in 12, 703 tons of rock "must be 

 annually kaolinised, and the whole of the alkalies removed in 

 solution." It seems to me that a metallurgist of Mr. Phillips' 

 experience should have known that the alkalies are never com- 

 pletely removed in kaolinisation. Tliat he is not acquainted 

 with the peculiar and remarkable conditions of the Comstock is 

 not surprising, for the lode receives but little attention, and that 

 of the most hasty kind, from visitors. I a>k your permission to 

 add the following summary of facts _which rebut Mr. Phillips' 

 criticism : — 



1. The removal of alkalies in subterranean kaolinisation, if it 

 is judged by the existing incomplete series of analyses, seems to 

 vary from less than one-fifth of the quantity of alkalies in the 

 present rock down to almost nothing. 



2. The whole results of kaolinisation are not represented in 

 the mine waters. In the vast areas of dry rock alteration has 

 beeu extensive, and seems to be going on now by means of 

 water-vapour, and none of this action supplies alkalies to the 

 mine waters. 



3. Thejliberation of hot gas which is an accompaniment of 



kaolinisation by atmospheric waters conveys the heat produced 

 in the dry areas to all parts of the mass, and especially to such 

 channels as watercourses and mine-openings. 



4. Kaolinisation in the Comstock region is not produced by 

 the action of cold water on cold rock, but by the combination 

 of water and rock, both already heated before the action to very 

 nearly the temperature they attain after it. The heat of the rock 

 is cumulative, its present temperature being mainly the result 

 of ages of previous kaolinisation, the heating effects of which were 

 preserved from dissipation by a blanket of rock 1,000 feet thick. 

 The \yater which takes part in the action at existing depths of 

 the mine has been heated by its percolation through 1,000 to 

 1,500 feet of hot rock lying below the blanket spoken of. Mr. 

 Phillips calculates that 85' are added to the temperature, but in 

 fact the actual increment of temperature by kaolinisation is, in 

 the locality given, but a small fraction of this quantity. Con- 

 sidering the small rainfall of Nevada, and the depth at which the 

 waters are now drawn from the rocks, and the perfect correspon- 

 dence of depth and temperature, it is more probable that the 

 actual gain of heat does not exceed one or two degrees, and may 

 even be less. 



5. Mr. Phillips' calculation that 330 tons of water are heated 

 by the kaolinisation of one ton of rock has no foundation in the 

 known facts, but is probably more than 99 per cent, from the 

 truth. His further error in supposing that the increment of heat 

 is 85' F. instead of being in the neighbourhood of l", as is more 

 probable, relieves his criticism of whatever weight it might have 

 if it had been adjusted to the well-known facts of the case, 



iij, Broadway, New York, June 17 John A. Church 



"On a Mode of Explaining the Transverse Vibrations 

 of Light " 



I VENTURE to call attention to what appears to me to be 

 (possibly) an objection to the views advanced by Mr. S. Tolver 

 Preston in his interesting article, " On a Mode of Explaining 

 the Transverse Vibrations of Light" (Nature, vol. xxi. p. 

 256). Mr. Preston's hypothesis I understand to be a special 

 modification of Lesage's, the speciality being that the cor- 

 puscles which by their impact on the cage-atoms of ordinary 

 matter cause gravitation, are also the carriers of some vector 

 property, the changes in which constitute radiant energy, and 

 that in fact there is no ether except just this assemblage of 

 minute corpuscles co-existing in the ultra-gaseous state {i.e., with 

 a mean free path of great length). Now, as far as I can see, 

 it is a strict corollary from this exceedingly fascinating hypo- 

 thesis that the velocity of propagation of gravity must be iden- 

 tical with that of light. In other words, the acceleration of a 

 material particle at any instant (I) caused by the attraction of a 

 second particle must be directed to the spot occupied by that 

 second particle, not at the instant I, but at some instant prior to 

 I, the interval between the two instants being the time taken by 

 the ultramundane corpuscles, and therefore by light, to travel 

 from the one particle to the other. But do not the observed 

 planetary motions necessitate the assumption that gravity, even 

 if propagated in time at all, is propagated with a velocity vastly 

 in excess of that of light ? At any rate this statement is fre- 

 quently met with in discussions on the nature of gravity, and is 

 much prized by advocates of "action at a distance." If it is 

 true, does it not constitDte a fatal objection to Mr. Preston's 

 hypothesis? 



Some two years ago it occurred to me that the ether might 

 consist of particles in the ultra -gaseous state, and might thus, in 

 accordance with Lesage's hypothesis, give rise to the mutual 

 gravitation of the grosser atoms immersed in it. I was then 

 unaware of the late Prof. Clerk Maxwell's suggestion that these 

 particles, by being the carriers of some vector property under- 

 going periodic reversal, might account for the propagation of 

 light ; and vaguely hoped that it might receive some explanation 

 from the fact, also discovered by Clerk Maxwell, that a body in 

 the ultra-gaseous state behaves like a sjlid towards any confining 

 boundaries to the extent that, like a solid, it opposes a certain 

 resistance to change of shape. But I deemed the whole theory 

 to labour under the fatal objection of uot giving a sufficient 

 velocity of propagation to gravity. 



I write in the hope that Mr. Preston or another of your 

 readers wdll inform me whether my objection is a valid one. 



J. W. Frankland 



Re^-istrar-General's Office, Wellington, New Zealand, May 6 



