Veins. * I. Breadth or width of veins.—In moft metalli ferous mountains, we find that veins extend a few hundred fathoms, and then their width does not exceed two feet. Veins whofe width exceeds a few fathoms are to be confidered as uncommon, and thofe whofe width is ftill greater, are to be viewed as excep tions to their general appearance. Humboldt and Friesleben obferved veins of calc-fpar 140 feet wide, traverfing gneifs, in the valley of Lauterbrun, in the Alps of Switzerland. In the iflanfi of Ar- ' ran, I obferved a vein of porphyry-flate nearly 160 feet broad, traverfing fandftone. Born mentions, that the Spitaler vein at Schemnitz, in Hungary, is from 14 to 15 fathoms wide. In that part of the Fichtelgebirge that belongs to Bavaria, there is a vein from 42 to 70 feet wide j and in the county of Holberg, near Rotleberode, there is a vein of fluor-fpar 35 feet wide. In this country there are veins of pitchftone and greenftone from 10 to 100 feet wide. The width of veins does not continue the fame throughout, but changes confiderably, and in fome particular veins in a remarkable degree. 2. Length of veins.—Veins differ very much in their length : when their length exceeds 6000 feet, it is to be confidered as uncommon. The follow ing may be mentioned as inftances of veins of uni common length: The Hallbriickner-Spath near Freyberg, which has been traced above four mile* and