Page:The Journal of geology (IA journalofgeology11893univers).pdf/76

and relatively so ineffective in structures whose delicate anatomy can still be traced even to microscopic details? Thin section of limestone which show a mass of interferant crystals suggest that this was to primary structure of the rock, and organic remains appear to be foreign bodies which are accidentally of the same substance as the matrix. If this view be correct, then only the alteration of the organic carbonate is the measure of the alteration of the rock-mass. If it can be shown that limestones now forming by chemical precipitation possess a crystalline structure, which resembles that of ancient limestones, the resemblance will constitute a presumption in favor of similarity of origin for the modern and ancient formations. And the fact that limestone is now being precipitated would, if it be established, leave the geologist free to weigh the evidence in the case of any ancient limestone for and against its organic or chemical origin. It is not proposed here to argue that limestones are prevailingly of one origin or the other, but only to show that the assumption of organic origin for all the calcareous deposits of the stratified series is too sweeping. To this end it is desirable to consider the chemical and mechanical conditions which affect the precipitation of carbonate of lime, to estimate the solubility of the carbonate in salt water, to review the conditions under which lime is contributed to, and distributed in, the sea, and to describe several cases of modern limestone formation by precipitation.

Schloesing made a number of experiments on the solubility of carbonate of lime in carbonic acid and water; he thus describes his method and results.^[1]

"Experiments:—The method adopted was to cause to pass through pure water, which was maintained at a constant temperature and contained an excess of carbonate of lime, a mixture of air and carbonic acid, of a composition varied at will, but constant, for each experiment; this mixture was constantly supplied until a perfect equilibrium was established between the substances