Incoherent matter is singular; D'Aubuisson ("Traite de Geogn. " tome 1 page 318) remarks on this circumstance. ) or of an argillaceous tuff; in this latter case the external crust was quite thin and hard. Some of these spherical balls were encircled in the line of their equators by a necklace-like row of smaller concretions. Again there were other concretions irregularly formed and composed of a hard compact ash- coloured stone with an almost porcelainous fracture adhesive to the tongue and without... read more
