Dec. 31, 1885] 



NATURE 



197 



the author still holds to the opinion that the form- 

 ation is an Eocene one. A larger part of the 

 work is occupied with descriptions of the Green 

 River plants, chiefly from Florissant, an incredibly 

 rich locality. This is prefaced by a lucid description of 

 the beds, which exceed 300 feet in thickness, by Mr. S. 

 Scudder. They are principally volcanic ash accumulated 

 in one or more old lake-basins. These and most of the 

 other fossiliferous rocks are situated towards the top of 

 the Green River group, which is reckoned to be 2000 feet 

 thick. The flora contains 22S species, of which 152 are 

 from Florissant, and is referred by Lesquereux to the 

 Oligocene. It was originally thought by him to be Mio- 

 cene, but the detailed comparisons he has made between 

 it and that described by Saporta from Aix, in Provence, 

 prove that he is justified in putting its age further back. 

 Indeed it bears a marvellous resemblance to that of 

 Bournemouth, and had he been able to make comparisons 

 he would perhaps have assigned it a still earlier date. It 

 is a matter of the greatest interest to find in America a 

 flora corresponding to those of Aix and Bournemouth, 

 and not represented anywhere to the north. The last 

 pages are occupied with descriptions of some new Mio- 

 cene plants from various localities. The book is illus- 

 trated by fifty-nine coloured plates, and however we may 

 differ as to the value of the determinations themselves, 

 all will agree as to the great service rendered to science 

 by the publication of such an important mass of data for 

 future comparison. J. Starkie Gardner 



LETTERS TO THE EDITOR 



[ 7 he Editor does not hold himself responsible for opinions expressed 

 by his correspondents. Neither can he undertake to return, 

 or to correspond 'cuith the writers of, rejected manuscripts. 

 No notice is taken 0/ anonymous communications. 



[ The Editor urgently requests correspondents to keep their letters 

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 that it is impossible otherwise to insure the appearance even 

 of communications containinginterestins and novel facts.'\ 



The Coal-Dust Question 



On several occasions during the Last five years, Sir Frederick 

 Abel has referred to the history of the coal-dust question, 

 and to my connection therewith ; and .as his views on this sub- 

 ject do not altogether correspond with mine, I desire, with your 

 permission, to state in this place how much, and in what 

 particulars, I differ from him. 



In his address to the Society of Arts, delivered on the 17th 

 of November last, Sir Frederick says: "Several well-known 

 French mining engineers published, many years after Faraday 

 and Lyell wrote, observations and experimental results as new, 

 which were simply confirmatory of those philosophers' original 

 statements and conclusions, and to some extent this was also 

 the case in still more recent publications in this country by 

 Galloway and Freire-Marreco." 



Faraday and Lyell's statements and conclusions were to the 

 following effect : — 



1. Fire-damp is not the only fuel in an explosion. 



2. The coal-dust is swept up by the blast and is partially 

 burnt. 



3. (Speaking of Haswell Colliery explosion)' "There is 

 every reason to believe that much coal-gas was made from this 

 dust in the very air itself of the mine, by the flame of the fire- 

 damp, which raised and snept it along, and much of the carbon 

 of this dust remained unburnt only for want of air." 



That is to say, the flame of the fire-damp is extended, and the 

 effect of the explosion is aggravated by the presence of the 

 coal-dust. 



" Phil. Mag., 1845. 



The Committee of the Coal Trade, who replied to Faraday 

 and Lyell's report in a letter dated February 7, 1845, ^° "°' 

 appear to have thought those authors' remarks about coal-dust of 

 sufficient importance to be noticed at all. Nor do the authors 

 themselves seem to have attached any particular importance to 

 them save as a record of a curious physical and chemical fact ; 

 for after making them they immea lately turned, like all their 

 predecessors and most of their successors, to the contemplation 

 of imaginary magazines of fire-damp a* a means of accounting for 

 the explosion. Moreover, both of them lived for many years 

 afterwards, during which one great explosion occurred after 

 another, and yet we do not find that either of them ever lifted 

 so much as the tip of his little finger to point to coal-dust as 

 the probable cause of the catastrophes. 



In 1855, M. du Souich, Ingenieur des Mines, said,' "A sort 

 of crust of light coke, which could be gathered from the timber 

 at various points, could only have origin.ated from the coal-dust 

 swept up in the working places and carried to a distance by the 

 extremely violent air-current caused by the explosion. This 

 dust being itself partially inflamed could continue the effects of the 

 fire-damp by carrying them further" {pent continuer les effets du 

 grisou en les portant plus loin). 



In 1861,= M. du Souich and M. Estaunie again insisted on 

 the same thing in similar terms. 



In 1867,^ M. du Souich again developed the same opinions. 



In iS64,*Vcrpilleuxde Reydellet, A. Buiat, Poumairac Baretta 

 and other engineers emitted opinions similar to the foregoing. 



In 1875,5 M. Vital wrote, "Extremely fine coal-dust is a 

 cause of danger in dry working places in which shot-firing is 

 carried on ; in well-ventilated workings it may of itself alone 

 give rise to accidents ; in fiery workings it increases the chances 

 of an explosion, and when an accident does occur it aggravates 

 the consequences of the fire-damp flame " (coup defiu). 



In 1875, 'i MM. Desbief .and Chansselle gave a short historical 

 resume similar to that of M. Haton, and quoted an opinion of 

 M. Verpilleux which appears to resemble my own, but has 

 never, so far as I am aware, been put prominently forward by 

 the author nor supported by experimental or other prooi^, namely : 

 " M. Verpilleux, who attaches great importance [importance 

 capitate) to coal-dust, was one of the first to call attention to it ; 

 comparing a fire-damp explosion to the detonation of a gun, he 

 went so far as to say that the dust represents the powder and 

 the firedamp the priming." 



In March, 1875, Sir Frederick, then Professor, Abel, address- 

 ing an audience at the Royal Institution on the subject of 

 "Accidental Explosions," referred to explosions in mines, and 

 mentioned the researches that had been made by Mr. R. H. Scott 

 and myself up to that date. He also speaks of dust explosions in 

 flour mills, &c. ; but, as showing the small importance he 

 attached to anything that had been previously said or done in 

 regard to coal-dust, it is remarkable that he does not even 

 refer to its existence. 



1 had been investigating the subject of great colliery explosions 

 since the year 1870, but had been unable to discover any ex- 

 planation of their occurrence wholly satisfactory to myself. At 

 the commencement of my work I h.id read all, or nearly all, 

 the English literature connected with it then extant, and amongst 

 other things the report and article of Faraday and Lyell on the 

 Haswell Colliery explosion, and the reply of the Committee of the 

 Coal Trade ;' but, so little impression did Fai'aday and Lyell's 

 remarks about coal-dust make upon me at the time, that I 

 afterwards forgot I had read them, and was only reminded 

 of the fact by seeing it recorded in an old note-book of my own 

 some time after the publication of my first paper. I retained the 

 impression, however, for in the paper * referred to I wrote : ' ' The 

 accounts of colliery explosions published in this country hardly 

 ever allude to the existence of coal-dust ; and when they do so, 

 in one or two cases [it should have been one case only] it is for the 

 purpose of suggesting that the gases disengaged from it by the 

 heat of the fire-damp flame would no doubt be ignited and tend 

 to increase the force of the explosion." 



It did not for a moment occur to me that this, which is Fara- 

 day and Lyell's view, could ever be accepted as an explanation 

 of the phenomenon I was trying to elucidate. 



' " Rapport de M. Haton de la Goupilliere : Des Moyens propres ;i prevenir 

 les Explosions du Grisou," 1880. 



2 Ibid. 3 md. t Ibid 

 5 Annates des Mines, 1875. 



<s Cotnptcs rendus des Reunions jnensttclles de Saint Etienne, June, 1875. 

 7 Iron, June i, 1878. s proc. Roy. S'c, 1876. 



