Geology, 467 



the occurrence of charcoal in coal measures and other mineral strata. In 

 the anthracite mines of North America, for example, wood charcoal occurs, 

 with the ligneous structure as well marked as in charcoal recently pre- 

 pared. — J, R. 



Volcanoes. — It is remarkable that in the old continent the principal 

 chains of mountains contain no volcanoes, and that islands and the extre- 

 mities of peninsulas are alone the seats of these ; while, in the new world, 

 the immense range which runs along the shore of the Pacific Ocean pos- 

 sesses more volcanoes than are to be met with in the whole of the old 

 continent and its adjacent islands. — J. R. 



Trachyte. — What was formerly denominated Trap-porphyry is now 

 called Trachyte, and is a granular fissured rock, formed of glassy felspar and 

 hornblende, in which augite, mica, laminar felspar, and quartz, also occur. 

 All the summits of volcanoes are composed of this- rock, whether they be 

 low hills, like those of Saxony, or rise, like the Andes, to 17,70iD ft. high ; 

 the latter, probably, situated on a crevice traversing the whole continent, 

 over an extent of 105 geographical leagues, from the Pacific to the Atlantic 

 Oceans. {Humboldfs Tabl. de la Nature.) 



Chemical Powers of Magnetism. — The following experiment is by the 

 Abbe Rendu. If a bent glass tube be filled with the tincture of red cab- 

 bage, and two iron wires suspended to the poles of a magnet be immersed in 

 the liquid in the two branches, the tincture will, in a quarter of an hour, 

 become blue, or of a deep green in both branches of the tube, although the 

 magnetism of the two wires must be of different kinds. The same result 

 is produced, if well tempered and polished steel needles be used in place of 

 the wires. If one wire be removed, the effect takes place only in the other 

 branch of the tube where the wire remains. The same results occur if the 

 wires are not in contact with a magnet ; but being then cleaned, they are 

 found to have become magnetic. Tincture of litmus undergoes similar 

 changes, but far more slowly, and the colour becomes green only in the leg 

 containing the north wire. 



M. Biot considered that the oxidation of the wires might in these produce 

 the ordinary effects of a voltaic current, but that as magnetism exerted its 

 influence, notwithstanding the presence of interposed bodies, he advised M. 

 Rendu to separate the wires from the tincture, by glass tubes closed at 

 their lower extremities. In this case, even according to Rendu, the same 

 phenomena were produced, but much more slowly. The tincture of red 

 cabbage, however, became perfectly green in two days. Mem. de Savoie. 

 Bull. Univ. A.x. 196. {Brande's Quart. Journal, Oct.— Dec. 1828, p. 429.) 



Scottish Gold. — It is a prevalent opinion amongst the peasantry in Scot- 

 land, that gold may be discovered by examining the sheep which feed on the 

 pastures where it is subjacent. The following are the supposed effects of this 

 sort of pasture, as" given in Bellenden's translation of Boetius's Cosmogra- 

 phe of Albion: — "The sheep that gangis [pastures] on Dundore are yellow; 

 their teeth are haed like gold ; their flesh red, as it were littit [dyed] with 

 saffron ; their wool is on the same manner." Cordiner, in his Picturesque 

 Antiquities, also mentions this hill, which is in the north of Scotland, and 

 spells it Dun d'Or, " the hill of gold." The people, he adds, assert that 

 the sheep have their teeth beautifully gilded. — J. R. 



Lead Ore. — Miners, supposing blende to be changed into lead glance, 

 talk of a mine's not being n^;e. This is improbable ; but a mine may be too 

 ripe, as appears from an instance at Lead Hills in Scotland, where the vein 

 which now contains the carbonates, sulphates, and phosphates, must once 

 have been replete with the more valuable sulphuret of lead. {Haidinger in 

 Edin, Phil. Trans., xi. 75.) 



