116 On Fire Damps in Mines, &c. 



have joined to the hexa-tetrahedron ia order to change it into 

 a pyramidated hexa-tetrahedron. Tlie result of this combina- 

 tion is a polyhedron with 24 summits and 80 triangular faces. 

 I shall give it the name of octocontahedron. 



[To be continued.] 



XXI. On Fire Daitips in Mines, &fc. 



To Mr. Tilloch. 



Sir, — 1 HAVE to regret that none of the many practical coal 

 masters, viewers, or agents, who aje readers of your useful work, 

 have attended to the requests that I ventured to address to them, 

 in page o03 of your last volume, for communications on the 

 causes and prevention of the enormous evils arising from^re- 

 dnmp in coal mines. Since then I have read in a periodical 

 work, to which I there alluded, a long paper by the Editor, giving 

 a Geognostical Sketch of Northumberland, Durham, &;c. — on 

 which I beg to remark, that most of the facts therein mentioned, 

 which arc useful, and numerous others such, respecting the geo- 

 logy of this district, were already before the public, in the sections 

 and writings of Millar, Forster, Bailey, Farey, Wynch, &c. ; but 

 of whose prior labours in the same field, not a hint escapes the 

 learned Editor : he has however thought proper in a long note 

 (written in his peculiar manner) to notice my former letter to you, 

 referred to above; and assuming therein, without sufficient rea- 

 son, that his Newcastle correspondent and myself meant to 

 assert, that sulpkuretttcl hydrogen gas occasioned the repeated 

 explosions in Felling Collierv ; proceeds to sav, " Now I do not 

 sec, how iron pyrites can contribute to the formation of carbu- 

 ret ted hydrogen ;" a thing never asserted by us, but, tha.i probably 

 pyrites and bad small coals might contribute to the dangerous 

 accunmlation of inflammable gas ; being well aware that a part of 

 it, at least, issued ia blowers or jets, from newly opened joints 

 in the coal and in its roof and floor, as Mr. Buddie has so well 

 described. 



The geognostical sketch alluded to, mentions, among the late 

 discoveries of its author in the mines of this district, that cubes 

 of fluor spar have been entirety removed therefrom, without his 

 being able to tell how or where; he says, "The change took 

 place in the centre of the vein, a hundred fathoms below the 

 surface of the earth, surrounded o« all sides by walls of solid 

 stone !, and quite impervious both to tdr and 7noistnre !" He 

 mentions also, iciole-like mas?,es oi J'used galena, being iouixd 

 suspended in cavities in some of the veins ; that in some districts 

 (thoup;]i 7io! ill this) ;i coke,-like state of the coals was obser\'ed, 



where 



