viii PREFACE 



vestigations of the "Hyatt School" of Palseontologists. Later, at 

 Harvard University, under the leadership of the unforgettable 

 Shaler, and guided by that keenest of analysts, William Morris 

 Davis, and by the others of that brilliant coterie of Harvard Ge- 

 ologists and Palseontologists — Wolf, Wood worth, Jackson, Ward, 

 Daly, Jaggar, and others — the principles of Lithogenesis. Glypto- 

 genesis, and Biogenesis formed daily topics of discussion, and 

 many of that group of eager students, who took part in these dis- 

 cussions, here laid the foundations for subsequent achievements in 

 these fields. It was at this time also that we in America first be- 

 came acquainted with those monumental contributions to Litho- 

 genesis and Biogenesis, that had been and were being made by the 

 then Haeckel Professor of Geology and Palaeontology at Jena, Dr. 

 Johannes Walther, now Professor of Geology and Palaeontology at 

 Halle. The Einleititug in die Geologic als historische IVissenschaft 

 had appeared only a few years before, and its influence in shaping 

 geologic thought, especially among the younger men, was just be- 

 ginning to be felt. The Lithogenesis der Gegenwart presented such 

 a wealth of facts concerning the origin of sedimentary rocks, that 

 attention began to be diverted from the problems of the igneous 

 rocks which had heretofore almost exclusively occupied petrog- 

 raphers, and "Sediment-Petrographie," or the petrography of the 

 sedimentary rocks, attracted more and more of the younger geolo- 

 gists, especially in Germany and France. In the latter country the 

 works of Cayeux and Thoulet led the way, while in Britain Mackie 

 and Goodchild applied the principles of eolian deposition to the in- 

 terpretation of British strata, and Sorby, Phillips and many others 

 accumulated a wealth of facts and inferences. 



It was at this period, too, that the attention of geologists and 

 especially stratigraphers was first seriously directed toward the 

 desert regions of the world and the phenomena of extensive sub- 

 aerial deposition. Here, again, Walther led the way in that classic, 

 Die Denudation in der Wiiste, followed in 1900 by his epoch-mak- 

 ing book. Das Gesets der Wiistenbildung, which, in its revised 

 second edition, appeared in 1912. It is, of course, true, that impor- 

 tant studies of desert regions were made earlier, notably those of 

 von Zittel on the Libyan desert (1883), but the significance of the 

 desert deposits in terms of stratigraphy was first fully appreciated 

 within the last decade. That the importance of the desert as a 

 geological factor has become widely recognized,, is shown by the 

 numerous recent studies, especially those on the Kalahari by Pas- 

 sarge, and those on the Asiatic deserts, by Sven Hedin, Pumpelly, 

 Huntington, and others. 



