SOME FACTORS AFFECTING THE DEVELOPMENT 

 OF MUD-CRACKS 1 



E. M. KINDLE 



Geological Survey of Canada, Ottawa 



INTRODUCTION 



Casual examination of the apparently erratic lines known vari- 

 ously as mud-cracks, sun-cracks, and shrinkage-cracks affords little 

 promise of results of interest from their systematic study. The 

 great geologic interest which these products of desiccation possess 

 in connection with the history of formations in which they occur 

 should nevertheless encourage the geologist to ascertain what effect 

 variation in the conditions under which they are formed will have 

 on the resulting kind or type of mud-crack. With the object of 

 ascertaining the nature and extent of the modification of the type 

 of mud-crack which may result from varying the conditions of its 

 formation, I have carried out the laboratory experiments described 

 below. These have been planned with a view to discovering (a) the 

 relative effects of rapid and slow desiccation on the same mixture, 

 (b) what influence, if any, composition of the mud has upon the 

 mud-cracks, (e) the possibility of producing parallel mud-cracks, 

 and (d) the differences which distinguish saline from fresh-water 

 mud -cracks. 



EXPERIMENTS 



Two kinds of clay have been used. In experiments i and 3 a 

 mud was used which came from the bottom of Lake Ontario, at 

 a depth of 630 feet, and represented very fine-textured material. 

 The other experiments were made with blue marine clay of Pleis- 

 tocene age from the Ottawa valley near Ottawa. This is also a 

 very fine-textured and tenacious clay. 



Experiment 1. — Lake clay which was thoroughly mixed with 

 about 5 times its volume of fresh water was poured into two 



Published with the permission of the Director of the Geological Survey of 

 Canada. 



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