Doctor Vaughan has asked me to say something of the problems that have arisen in my studies of sedimentary formations, and the kinds of research that are needed in their solution. I will dwell on but one phase in sedimentation, but this is a most important one, though seldom taken up seriously by students of stratigraphy or by oceanographers. I refer to diagenesis, or the chemical and physical changes that sediments undergo during and after their accumulation, but before consolidation takes place. Diagenesis, therefore, has nothing to do with the later metamorphic alterations superimposed by orogeny and intrusive rocks. It is strange that this subject is so rarely studied, since it was as long ago as 1888 that Gümbel directed attention to these changes and coined the word. On the otlur hand, Walther in 1893 devoted a long chapter to diagenesis in his “Einleitung in der Geologie” (pages 693–711), . . .