PREFACE.

THIS Work was undertaken, and had in part appeared in the pages of a periodical publication, when there was rather a dearth of elementary treatises on geology, and before so many had been sent forth by some of the first geologists of the age, that to add to their number may perhaps appear superfluous, if not presumptuous. Its extension and publication, in a separate form, has been determined on, because it is hoped that it differs sufficiently in its plan from any of its predecessors, to render it a humble but useful auxiliary to works which it does not aspire to supersede.

It has been said that a man may be too consummate a mineralogist to make a good geologist, or, in other words, that the constant study of minute details, necessary for the discrimination of individual minerals, unfits the mind for the apprehension of the sublime generalizations of geology; but, on the other hand, it is no less true, that a certain amount of mineralogical knowledge is an essential requisite to the successful str of that science. It is usual for the authors of elementary geological books to assume that their readers possess this knowledge, or to refer them for it to arranged cabinets and oral instructors, and there can be no doubt that they who have such advantages within their reach will find in them the readiest

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