DISCUSSION 4oi 



to cooperate in the iiivestioatioiis wliieli it is proposed to take up. I refer 

 to engineers in eliarge of dredging operations and the construction and 

 maintenance of liarhor structures. Although not geologists, there is 

 prohahly no group of men more vitally interested in sedimentatiou than 

 those engineers to whom is entrusted the work of keeping our harhors 

 open and of certain depths. T know from personal association their keen 

 interest in luany of the prohlems we propose to take up. 



It is most ])rohahle tliat one of tlie practical l)yproducts of the pro- 

 posed researclies in sedimentation will he the accumulation of much (Uita 

 of vital importance to those engineers who are intimately concerned with 

 the prohlems of inshore sedimentation. 



L. D. BuRLixG : The problem of researches in sedimentation is funda- 

 mental and so large that I shall confine my remarks to the particular 

 suggestion made by ]\[r. Shaw as to the collection of rock specimens illus- 

 trating the ])rocesses, types, and results of sedimentation. If my own 

 experience is typical, and it is probably no more than this, we all have 

 in our own collections numbers of specimens which may have larger im- 

 portance and wider significance than we now think. A start in the direc- 

 tion of following out the suggestion made by Mr. Shaw could be made by 

 the assembling of this scattered material into the larger museums or in 

 the hands of special workers in the problems involved. Certainly there 

 is just as much reason for assigning the name of type to a specimen used 

 as the basis of a description of a new type of oolite, and for its preserva- 

 tion in a museum, as there is in the case of a fossil. 



Among my own collections is a specimen of limestone permeated along 

 bedding planes by series of tabular dolomite crystals which may even 

 entirely replace the limestone in particular localities. The general drift 

 toward the hypothesis that dolomitization is essentially contemporaneous 

 with deposition may receive confirmation or refutation as a result of the 

 careful study of such a specimen as the one described. 



J. B. WooDWORTH called attention to the necessity of understanding 

 the laws of contrast in coloration of rocks. He also called attention to 

 Xewberry's doctrine of ternary succession of strata in marine formations, 

 the recognition of which has since been found in the Comanchean of 

 Texas and the Upper Cretaceous of the Great Plains by Lee. 



D. F. IIkwett: In considering the materials that make up sediment- 

 ary rocks, many geologists overlook the direct contributions from vol- 

 canic sources. This is largely due to the obscurity of the evidence of the 

 origin. Close examination recently of numerous specimens of sediments 

 from the Mesozoic and Tertiary sections of northeastern Wyoming showed 

 that volcanic materials are common and locally make up 5 to 10 per cent 



