CONSOLTDATTOX OF MARINE DEPOSITS 429 



intraformatioiial limestoiio hroccias wo know that the bedded lime iiuids. 

 up to one incli tliick, became siin-craeked and liardened to rock in tlie 

 course of at most a few months. Apparently, then, drying out brings 

 on quick solidification through cementation, but if formations remain 

 constantly wet, when do they beccmie shale and limestones? These are 

 some of the problems to be answered by the rising school of stratigraphers. 



Discussion 



G. E. Mansfiklo: In a recent economic study of New Jersey green- 

 sands I had occasion to make a number of borings and to collect samples 

 of greensand from the top to the bottom of the deposit at a number of 

 places. Mechanical analysis, including wet and. magnetic separations and 

 sizing operations, were carried out. Some of the material contains much 

 "clay"' or colloidal matter, which analysis shows contains about as much 

 potash as the actual glauconite grains. It seems probable analyses, not 

 yet completed, will show this substance to be colloidal or amorphous 

 glauconite. Some of this material may have been formed by mechanical 

 wear of the glauconite grains, but some may represent amorphous glau- 

 conite not yet formed into actual grains. The grains themselves show 

 little resemblance to foraminifera, and it seems likely that some grains 

 may have been formed or may now be forming from the amorphous 

 glauconite. I have been unable to identify such grains or to detect them 

 in formation. This phase of the problem might appropriately be consid- 

 ered by the physical chemist. 



M. W. TwiTCHELL called attention to the need of further investiga- 

 tions of the microscopic life found in sediments — ^diatome, foraminifera, 

 radiolaria, etcetera, determining characteristic or diagnostic forms or 

 groups of forms. This is especially important to the student of well 

 samples, well records, correlation of well sections, etcetera. 



W. H. Twenhofel: Before sedimentary rocks can be studied and de- 

 scribed so that a reader may obtain the most from what is written, there 

 must be precision of definition. Sands are described as fine, medium, 

 and coarse grained. The terms mean different things for every student 

 and different things for the same student at different times. The color 

 of rocks is given as drab, buff, gray, etcetera, and no other than the 

 person who applied the color has any clear conception of what the term 

 means, and even he is apt to have forgotten when his memory of its 

 occurrence becomes dim. 



Sediments, both those non-forming and those consolidated into rocks, 

 should be studied from the point of view learning to what extent the 



