ABSTRACTS OF PAPERS 23 



seems worth while, even if the ultimate object in view should prove impossible 

 to attain. Studies of this kind would, without doubt, result in learning much 

 about sedimentation that we do not now know. The conditions under wliich 

 sedimentation takes place have infinite variations. This much we can see 

 from the great variety of sedimentary rocks showing innumerable differences, 

 such as in texture of the clastic elements, in the size and composition of these 

 elements, in their mingling and sorting, and in their lamination and bedding. 

 These different characters, without any doubt, maintain certain relations to 

 each other. What these relations are is a subject concerning which we have, 

 as yet, very little information. 



So far as I know, the only rhythms that have hitherto been noted in sedi- 

 mentary deposits are the diurnal and the seasonal rhythms. There is at least 

 one other cycle which may be found to appear in sediments. This is the 

 twelve-year cycle of the sun-spot period. It seems to be fairly well estab- 

 lished that precipitation in the United States is influenced by this cycle at the 

 present time, and it may very well be that under certain general and world- 

 wide climatic conditions the effect of this period may have been sufficiently 

 marked to become apparent occasionally in sediments showing annual layers. 

 Should such be the case, the appearance of this cycle would aid in identifying, 

 and perhaps also in observing, the annual cycle. May there not also be other 

 larger climatic cycles, such as cause variations that have been observed in the 

 advances and recessions of ouf continental glaciers? 



Everything considered, it seems correct to regard stratification in sediments 

 as marks of time. The layers separating the ledges of limestone, so familiar 

 in the quarry, are the most common features of stratified rocks. What do 

 these signify? Is it likely that they are haphazard phenomena? I cannot 

 believe that. A closer study of the details of stratification in sedimentary 

 rocks, I believe, can not fail to give important results relating to more accurate 

 estimates of geologic time, expressed in years. Even if we should be able to 

 observe interpretable stratification only in scattered parts of the stratlgraphic 

 column, as seems most probable, we can expect that these will give us data 

 invaluable to those who shall make a special study of time in geologic history. 



Discussion 



Prof. A. C. Lawson : It is necessary to discriminate carefully between ap- 

 parent and real rhythm in sedimentation, in any effort to apply rhythm to the 

 measure of geological time. The radiolarian cherts of the coast ranges of 

 California afford a very fine example of apparent rhythm which is very prob- 

 ably not an expression of rhythm in the sedimentary process. The work of 

 E. L. Davis, of the University of California, has shown that such an apparent 

 rhythm may be produced in a beaker on the laboratory table. 



CHEMICAL AND PHYSICAL RESEARCHES ON SEDIMENTATION 

 BY ROGER C. WELLS * 



(Abstract) 



The work of this svibcommittee was carried on by conferences between the 

 chairman and individual members of the committee. Tlie information ac- 



^ Introduced by T. Wayland Vaiighau. 



