Certain waters, after dissolving calcareous substances by means of the superabundant carbonic acid with which they are impregnated, allow these substances to crystallize after the acid has evaporated; and, in this manner, form stalactites, and other concretions. There are strata, confusedly crystallized in fresh water, which are sufficiently extensive to be compared with some of those which have been deposited by the ancient sea. The famous Travertine quarries of the neighbourhood of Rome, and the rocks of the same substance, which are formed, and continually varied in figure, by the river of Teverona, are generally known. These two modes of action may be combined; the deposits accumulated by the sea may be solidified by stalactite. Thus, when springs abounding in calcareous matter, or containing some other substance in solution, happen to fall into places where these deposits are formed, we then find aggregates in which marine and fresh-water productions may be blended. Of this description are the banks in the island of Guadeloupe, which, along with human skeletons, present land and sea shells mingled together. Of the same nature also is the quarry described by Saussure, in the neighbourhood of Messina, in which the sandstone is seen forming by the consolidation of the sand thrown up by the sea.