Glacial Geology and the Pleistocene Epoch

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This informative book takes a comprehensive look at the subject of glacial geology in the Pleistocene Epoch, and is highly recommended for inclusion on the bookshelf of anyone with an interest in the subject. Preface: 'The Pleistocene epoch occupies a peculiarly important place in the time scale of geology, for it embraces the events of the latest million or more years in the history of the Earth and is therefore so recent that it bridges the gap between the geologic changes now in progress and the more remote past. "When the work of the geologist is finished", wrote Gilbert, "and his final comprehensive report written, the longest and most important chapter will be upon the latest and shortest of the geologic periods. The chapter will be longest because the exceptional fullness of the record of the latest period will enable him to set forth most completely its complex history. The changes of each period - its erosion, its sedimentation, and its metamorphism - obliterate part of the records of its predecessor and of all earlier periods, so that the order of our knowledge must continue to be, as it now is, the inverse order of their antiquity." This fact in itself furnishes an adequate reason for making the principal facts of the Pleistocene epoch compactly available, not only to geologists but also to ecologists, archeologists, geographers, and . others whose studies reach back into the prehistoric realm. In addition, the increased pace of research upon Pleistocene problems in general, and problems in glacial geology in particular, that has been evident during the last two decades has emphasized the necessity, in this field, of a summary that will be at once a reference to the data already established and a means of indicating the areas and problems in which further research is most needed. These are the principal objectives of the present volume. No one knows better than its author that it falls short of attaining them. Knowledge of the Pleistocene has grown to such an extent that a complete reference work would become an encyclopedia. The consequent necessity for condensation has required the exercise of selective judgment at every turn. The list of references at the end of the book is far from complete, though an earnest effort has been made to see that it is representative. In particular it may lack important titles that have appeared in some countries during the war years and that have not yet been widely distributed. This discussion treats the Pleistocene frankly from the point of view of glaciation, the outstanding characteristic that distinguishes the Pleistocene from the epochs that preceded it. The somewhat cumbersome title was selected with this fact in mind, in an effort not to create the impression that the work is a fully balanced treatment of every phase of the Pleistocene. As is pointed out in Chapter 16, the correlations of Pleistocene events cited and suggested are, as far as possible, those based on geologic evidence rather than on archeologic evidence. In the presentation of geologic evidence itself stream-terrace data are used as little as possible in the belief that this class of data is more frequently subject to faulty interpretation than the data obtained from features of other kinds. In particular this book avoids, in correlation, deduction from any theory of Pleistocene climatic fluctuation which sets up a fixed chronology of events. This conservative attitude is adopted on the principle that only when the stratigraphic column is built up strictly on geologic evidence can the influence of prejudice in favor of a particular theory of climate be avoided. To enable the reader to evaluate the reliability of the data used, a continuous effort has been made to discriminate between reasoning by induction from field evidence and reasoning by deduction from assumed general conditions.