ROCKS. 2C9 



stratification existing between the porphyry and the argen- 

 tiferous ores in the Saxon mines, (the richest and most 

 important in Germany), that these formations are at any rate 

 more recent than the vegetable remains found in carboniferous 

 strata and in the red sandstone.* 



All the facts connected with our geological hypotheses on 

 the formation of the earth's crust, and the metamorphism. of 

 rocks, have been unexpectedly elucidated by the ingenious 

 idea, which led to a comparison of the slags or scoria) of our 

 smelting furnaces, with natural minerals, and to the attempt 

 of reproducing the latter from their elements. f In all these 

 operations, the same affinities manifest themselves, which 

 determine chemical combinations both in our laboratories 

 and in the interior of the earth. The most considerable part 

 of the simple minerals which characterise the more generally 

 diffused plutonic and erupted rocks, as well as those on which 

 they have exercised a metamorphic action, have been 

 produced in a crystalline state, and with perfect identity, in 

 artificial mineral products. We must, however, distinguish 

 here between the scoria) accidentally formed, and those which 

 have been designedly produced by chemists. To the former 

 belong feldspar, mica, augite, olivine, hornblende, crystallised 

 oxide of iron, magnetic iron in octahedral crystals, and 

 metallic titanium;; 1 ; to the latter, garnets, idocrasc, rubies, 



* Coustantin von Beust, Ueler die Porphyrgebilde, 1835, s. 89-96 ; 

 also his Bdeuchtung der Werner schen Gangtheorie, 1840, s. 6 ; and C. 

 von Wissenbach, Ablildungen merkwilrdiger Gangverhdltnisse, 1836, 

 fig. 12. The ribbon-like structure of the veins is, however, no more 

 to be regarded of general occurrence than the periodic order of the 

 different members of these masses. 



t Mitscherlich, Ueler die kilnstliche Darstellung der Minerahen, in, 

 the Abhandl. der Akademie der Wins, zu Berlin, 1822-3, s. 25-41. 



+ In scorioe, crystals of feldspar have been discovered by Heine in the 

 refuse of a furnace for copper fusing, near Sangerhausen, and analysed 

 by Kerstcn (Poggcnd. Annalen, bd. xxxiii. s. 337); crystals of augite 

 iu scoriae, at Sahlc (Mitscherlich in the Abhandl. der Akad. zu Berlin, 

 1822-23, s. 40) ; of olivin by Scifstrom (Leonhard, Basalt-Gebilde, bd. ii. 

 8. 495) ; of mica, in old scorire of Schloss Garpenberg (Mitscherlich, in 

 Leonhard, op. cit. s. 506) ; of magnetic iron, in the scoriae of Chatillon 

 sur Seine (Leonhard, s. 441) ; and of micaceous iron, in potter's clay 

 (Mitscherlich, in Leonhard, op. cit., s. 234). 



[See Ebelmer's papers in Ann. de Chimie et de Physique, 1847 : also 

 Report on the Crystalline Slays, by John Percy, M.D., F.K.S., and William 



