XII PREFACE TO THE THIRD EDITION. and transition tracts of England and Wales have been investi gated in a far less degree than those of a newer origin. “ It has been said of crystals,” says the Abbe Haiiy, “ that they are the flowers of minerals ; an observation concealing a very just idea beneath the air of a comparison which appears to be only ingenious.” The importance of “ form will become more evident,” he further observes, “ if, in pursuing our inquiries into the niceties of the mechanism of structure, we conceive all these crystals as the assemblages of integrant molecules per fectly resembling each other, and subject to the laws of regu lar arrangement. Thus, although by a superficial notice of crystals we might adjudge them to be only the sports of nature, a more intimate acquaintance with them leads to this conclu sion,—that the Deity, whose power and wisdom prescribed the unerring laws of the planetary motions, has also established those which are obeyed with the same fidelity, by the molecules com posing the various substances concealed in the recesses of the Earth.” May 10, 1823. W. P.