294 



the stone of Igast is a slag of artificial formation, and consequently 

 the chemist Bornwasseh has missed the fragments of the real meorite. 

 H. Michel has however not solved the problem of the origin of 

 the slag. As far as I know, snch like slags do not occur in tile- 

 works, neither does the chemical composition agree with it. In glass- 

 works one will likewise look in vain for similar slags, quite apart 

 from the question, how such a by-product of industry can ever have 

 reached the isolated country-seat of Igast. Neither does the com- 

 parison with fulgurites, made by A. van Lasaulx, hold. 



In my opinion a plausible explanation can be found if we regard 

 the discovered fragments as proceeding from a rye-slag. C. Gkewingk 

 described the product of combustion and melting 6f a rye-stack as 

 a grey partly graphitic mass, having the appearance of lava or slag 

 of the hardness GVs') and A. Lagohio') added to this, that according 

 to the microscopic examination augite, graphite and orthoclase were 

 secreted, and that the appearance reminded of certain glossy modi- 

 fications of volcanic rock and of melling-i)iodiicls obtained by F. 

 FouQUÉ and A. Michel-Lkvy by an arliti -ial process. '') 



It is a striking fad, that II. Michkl likewise com})ares the micro- 

 scopic character of the stone of Igast with those products. The fact 

 that inclosures of quartz, microcline and j)lagioclase tliat do not 

 originally proceed from that slag, are found in the rock might be 

 thus explained, that the slag, when still in its li(piid state, has run 

 over sand so that the grains of quartz and microline were enclosed. 

 I must however acknowledge, tliat the grauiineous slags which I 

 had an opportunity of examining, did not show any resemblance 

 with the rock of Igast, neither did they show similarity with the 

 slag examined by A. Lagorio. The material proceeding from burnt 

 hay-stacks, served instead. As these stood on a clay-soil it can 

 easily be explained that the ijiclosed grains of sand were but i'ew 

 in number, but the secreted individuals of plagioclase, augite and 

 magnetite were neither met with. In the thin sections could be 

 discerned a light yellowish or greenish glass, in which locally 

 numerous microlites and sometimes tridymite-aggregates were secreted. 

 Of a similar nature was the slag formed by the combustion of 

 great masses of straw belonging to the straw-board-works "Union" 



-) Petrificirte Roggenkörner. Sitzungsber. Naturf. Gesellsch. Dorpat. 5. 2. 1879. 

 Dorpat 1880, p. 220. 



~) Zusammensetzung von Roggenschlacken. Ibid. p. 230. 



■^) Reproduction artificielle de feldspatlis ot d'une roche volcaniqiie complexe 

 (labradorile) pyroxénique, par voie de fosion ignée. Gompt. rend. Acad, des Sc. 87 

 Paris 1878, p. 781. 



