CHANGE OF FACIES 741 



was rarely applied to the extent that it might have been in the interpreta- 

 tion of the older rocks. This was especially the case where two facies 

 progressively replace one another. We all recall the Catskill- Chemung 

 discussions of two decades ago, and I remember well when the president 

 of onr Society, Dr. Clarke, announced at the Rochester meeting the discov- 

 ery of the eastward replacement of the Onondaga limestone by the Mar- 

 cellus shale, an announcement which to me opened broad vistas of corre- 

 lational possibilities, down some of which I have since adventured. That 

 such replacements of rock facies, with a corresponding replacement of 

 adapted organic types, rather than a succession of stratigraphic breaks or 

 hiatuses, explains many of the puzzling phenomena in our stratigraphic 

 columns is the growing conviction of students who approach the science 

 through the avenue of lithogenesis. The correlation of rock facies is, of 

 course, closely bound up with the question of the origin of the sediments, 

 and for this reason the determination of the source and the manner of 

 transportation of the material becomes a vital question. On this account 

 mechanical analysis of older deposits, based on the methods and principles 

 developed in the modern sediments, must take a prominent place in our 

 discussion, and it is a matter of congratulation that this problem, so aus- 

 jnciously inaugurated in this country by Goldman, is being vigorouslv 

 attacked by American geologists. i 



It may perhaps be acknowledged that in general we need be at no loss 

 for criteria by which to interpret a normal marine deposit of the littoral 

 zone, and that, too, w^e know by what tokens a certain rock is excluded 

 from the category of deep-sea sediments. And yet we can not be so cer- 

 tain that a foraminifcral rock like the white chalk or a pteropod ooze like 

 the Genundewa limestone, which sliow some of the most pronounced char- 

 acteristics of deep-sea oozes, are not after all shallow-water deposits. We 

 know^ too little of seashore sediments and the permanency or evanescence 

 of the structural features impressed upon them, and their chance of 

 preservation, to apply these criteria with certainty to the interpretation of 

 older sediments. Who can say what type of cross-bedding, if any, is 

 characteristic of the seashore? And who has established beyond cavilthe 

 conditions under which such structures are formed, and, above all, pre- 

 served? Of ripple-marks and beach-cusps we feel more certain, and yet 

 who can say what are the conditions necessary for their preservation and 

 what the conditions ininiical to it? And when we try to recognize an- 

 cient estuarine and lagoon deposits, where shall we find the infallible 

 characters 1)y which we may interpret these? And does this not apply 

 to deltas as well, though hero, perhaps, we stand on surer ground ? It is 



