ABSTRACT
Marble, then, is metamorphosed limestone. Since marble shares with limestone all the qualities that concern us, I shall, especially in the next chapter, often use the one term 'limestone' to denote them together. In any case, my subject centres around the purer kinds of limestone which, in some varieties, Istrian stone for example, approximate closely to marble. But all limestones, to greater degree than the other sedimentary rocks, and to a yet greater degree than the igneous rocks, possess a substance that provokes from water, the dominant natural carving force, a most palpable sculpture. Calcium carbonate or calcite, the basic mineral of limestone and marble, is almost insoluble in pure water: but nearly all water, including the fresh rain, holds carbon dioxide, which has the power, in some degree, to dissolve calcium carbonate. The most fantastic as well as
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