.MTA2Mw.NzIxMTg

219

practised at the present day, hit by the effect of calcination for some time in a slow red heat, This will derive glass, especially green glass, of its transparency, and render the surface white to a certain depth. The composition of the tube of glass seems to be simply a silicious sand, and an alkali, probably with a small addiction of lime and vegetable ashes. It is hard, and will not receive scratches?, like the lead glasses, whence it is concluded that there is no lead in the composition. Its colour seems also owing to the impurity of the materials employed, like that common window and bottle glass. And it is probably caused by a minute portion of iron in the state of an oxyde combined with the sand and alkali. The next enamel covering the tube, and the part in which these glasses were found, seem to have been constructed of similar materials, as they differ very little in colour, texture, or other external character. Possibly a very fusible brick clay, highly impregnated with oxyde of iron and pulverised fragments of green glass, are the principal ingredients of both. The earthen pot is manifestly constructed of different materials from those employed for brown pottery at the present period. It is a more imperishable material, and of a vitreous appearance. On Bis River, in the state of Missouri, a similar discovery