740 A. W. GRABAi;— INTERPRETATION OF SEDIMENTARY ROCKS 



port, under Sollas, and the studies of deep-water organic deposits by Mur- 

 ray and others of the Challenger expedition, and those of Ponrtales and 

 Agassiz in America, and by Krlimmel and otiier Europeans, the studies 

 of lime secretion and precipitation through the agency of algse by Mar- 

 shall Howe and Hothpletz, and through bacteria by Drew, Kellermann, 

 and Yaughan, indicate the lines of work which have been pursued. 

 Finally, the detailed study of terrestrial deposits of vegetal origin, such 

 as those of C. A. Davis and David White in this country, of Gunnar 

 Samuelson in Scotland and Scandinavia, and. of Eamann on the German 

 Moors, are of fundamental significance. The masterly treatise of Potonie, 

 '^Die Entstehung der Stein-Kohle und der Kaustobiolithe iiberhaupt,'' 

 which has already passed its fifth edition, furnishes the standard Euro- 

 pean reference work, as does the equally authoritative summary of our 

 present knowledge of coals and coal formations by our own J. J. Stevenson 

 for the English-speaking Avorld. Finally, w^e can not omit to mention the 

 promising investigations on the origin of coals recently begun by the 

 botanist Jeffre}^ in this country. 



The old]::r Sedimentaries 



So far I have been considering mainly the investigators among recent 

 sediments. The application of the kllo^vledge gained from these to the 

 interpretation of older deposits has been of slower development. From 

 the very first, students of sediments have been in the main maiinists, 

 though when the organic evidence pointed unmistakably to the presence 

 of fresh waters they resorted to a lacustrian variant. Even today the ui- 

 terpretation of sediments as of other than marine or lacustrine origin 

 meets with a good deal of skepticism in some circles, and the fiuviatilists 

 are not in much favor, especially when they intrude upon territory hith- 

 erto preempted by the marinists. When, in addition, they have the temer- 

 ity to carry an entire group of orgajiisms along with the sediments from 

 the sea into the rivers, they needs must possess the courage of their con- 

 victions, for they can not look to much support. Fortunately, however, 

 American geologists are the most tolerant of men, and even the most 

 startling ideas get a hearing if they are supported l)y facts and are tlie 

 result of logical reasoning. 



C 'RANGE OF FaCIES 



Although it was always recognized by students of jnodern marine sedi- 

 ments thai the facies of the dc^posit changes continually, this principle 



