64 PROCEEDINGS OF THE ANN ARBOR MEETING 



Experiments have shown that compression and flow produce parallel struc- 

 tures in both soft and hard materials, and the processes enumerated must 

 yield similar results in many homogeneous, fine-grained deposits. The efficacy 

 and mode of operation of some of the factors concerned are, however, but im- 

 perfectly known. Critical field observations and rigorous quantitative tests 

 are urgently needed. 



Read by title. 



DEVI'JLOPMEXT OF SHRIX KAO'E CRACKS IN SEDIMENTS WITHOUT EXPOSURE 



TO THE ATMOSPHERE 



]!Y W. H. TWENHOFEL 



{ Abstract) 



Experimental work in the laboratory with two types of sedimentary ma- 

 terials has show^n that shrinkage or mud-cracks develop in these sediments 

 without their being exposed to the atmosphere. Bentonite and powdered 

 hematite, the latter from Mayville, Wisconsin, were used, the latter in only 

 one experiment. The work with bentonite has been repeated many times and 

 has been sustained by field observations, so that the results appear certain. 



Presented extemporaneously. 



OBSERTATIONS OX THE RANGE AND DISTRIBUTION OF CERTAIN TYPES OF 

 CANADIAN PLEISTOCENE CONCRETIONS 



BY EDWARD M. KINDLE 



(Ahstract) 



The concretions described are from the Quaternai'y sands and clays of T.ab- 

 ]-ador, the Northwest Territories, and Ontario. 



The points discussed include the influence of the nucleus on the shape of 

 concretions and deductions from localized distribution concerning some of the 

 factors in their formation. 



Five types of concretions, Mdiich are primarily the product of lithologic con- 

 trol, are described from the Ottawa Valley. The stratigraphic range of these 

 several tjpes is indicated. 



Nomenclature suital)le for discriminating some of these types is suggested. 



Presented in full extemporaneously. 



Discussion 



Prof. T. T. Quikke: Certain surticial features on marlekor look like welts 

 oi- small raised ridges ; they may have been caused by the filling of shrinkage 

 cracks by hardened material, followed by continued shrinkage of the main 

 mass. Other concretion-like masses appear to have been formed by the rolling 

 of mud balls down clay slopes, with the result that they carry upon their 

 surfaces a sort of wrapping of clay layers about the central parts. 



