Professor GREYWACKE, the eminent Geologist, delivered an address on Natural Petrifactions, indicating the various specimens of Ancient Fossils by which he was surrounded, and describing their formation.

" I was now in a rude and barren country, presenting a strong contrast to the soft scenery I had left, and consisting of an elevated mountain plateau, or table land of slate of the Greywacke sort, the heights on the eastern side of the Rhine being of the same level, and the channel of the river appearing as a narrow valley, which the eye overlooks entirely.

Before sunrise we reached the summit of a narrow ridge, trending East-South-East 1/2 a mile east, from where the boats were lying: in this singular ridge I again noticed the dip to the south-east: it was composed of a variety of rocks, jasper, a greyish kind of flinty indifferent limestone, and greywacke.