736 ;A. W. GRABAU— INTERPRETv^TION OF SEDIMENTARY R0CK8 



metaniurphism of sediniejits have claimed atteution, and indeed to some 

 students all rocks are metamorphic rocks and have no other significance. 

 That metamorphism of some kind or other affects all rocks' from the 

 beginning, that indeed the material of which man^^^ sediments are made 

 is the product of metamorphism hy disintegration of older rocks, is 

 perfectly true. This and the changes .which rocks undergo as the result, 

 of normal maturation have long been recognized by the student of sedi- 

 ments as the phenomena of diagenism. But such phenomena, Avhile not 

 neglected— indeed often carefully considered— are of secondary impor- 

 tance when compared with the more fundamental problems of origin, 

 which have now begun to receive the notice they deserve. Again, where 

 formerly the secondary structures induced by disturbances and readjust- 

 ments attracted geological students, today the original structures of 

 rocks, or those produced iu the process of rock -making, have 1)egun to' 

 claim chief consideration. 



The early and aioke hecext Investigators of Sedimextaries 



In this return to the study of the rocks tiu^msehes from the considera- 

 tion which their distribution and age relations had previously claimed, 

 it was natural that attention should be largely centered on the crystalline 

 rocks, which, from their varied mineral composition and frequent com- 

 plexity of structure, offered an attractive field once the way was shown 

 by the invention made l)y William iSTichol and by the genius of Henry 

 Clifton Sorby. Sedimentary rocks, from their apparent simplicity and 

 relative uniformity, did not at first attract the new school of petrog- 

 raphers. The responsibility for this is perhaps to be laid at the door of 

 the two great continental masters in this field, Ferdinand Zirkel and 

 H. Eosenbusch ; but it should be noted that Sorby — ^the father of modern 

 petrography — was not unheedful of the problems offered by tlie sedi- 

 ments, and in 1889, and, again in his last work, published after his death, 

 he has given us a masterly treatise on certain phases coimected with the 

 . composition and structural characters of sediments. 



1^0 one, I think, will. dispute my statement that the science of "the 

 .petrogenesis of sediments naturally had its beginning in f he woi'k of 

 ,Prof. .Dr. Johannes Walther, who, while Plaeckel Professor of ,G.eoTogy 

 and Paleontology at .Jena, issued in 1893-1894 his masterly ''Einleitung 

 in die Geologic als Historische Wissenschaft." We are especially con- 

 cerned with the volume on "Lithogenesis der Gegenwart," which for the 

 first time brought tog^^ther the scatteredobservations and deductions on 



