136 E. M. KINDLE 



porcelain vessels of the same shape and size, each being completely 

 filled. One of these was set in direct sunlight when the daily noon 

 temperature exceeded ioo°, and the other was kept in the shade 

 until the water had evaporated and mud-cracks had developed. 

 The specimen exposed to sunlight developed mud-cracks on the 

 third day. The other vessel showed the first mud-cracks on the 

 eighth day. When completely dried, the mud in the two vessels 

 showed a very marked difference in the size and number of polygons 

 outlined by the mud-cracks developed. The sun-dried mud had 

 cracked into 6 irregular-sided polygons, while the same volume 

 of mud, which had been slowly dried in the shade during a period 

 about three times that given the direct sunlight specimen, showed 

 26 polygons. Rapid drying thus seems to produce comparatively 

 widely spaced mud-cracks, while slow desiccation gives closely 

 spaced mud-cracks. Some interesting incidental observations 

 were made in connection with this experiment on the tendency dis- 

 played by the very fine sand grains to segregate themselves from 

 the mass of the mud and to gather along the edges of the joints and 

 the margin of the vessels holding the mixtures. This segregation 

 of the sand grains resulted in a ring of sand around the outer margin 

 of the mud where it came in contact with the sides of the vessel. 

 Along the sides of many of the mud-cracks the upper angle of the 

 polygon was edged by a continuous border of sand. On the lower 

 side of the polygon edges the sand showed no tendency to segregate. 

 This segregation of the sand along the edges of the mud-cracks 

 appeared to be dependent in part upon the extreme fineness of the 

 grains. An attempt to repeat this phase of the experiment by 

 adding sand of average fineness to mud which was desiccated in the 

 sun failed to show any segregation phenomena, presumably because 

 of the larger size of the sand grains used. 



Experiment 2. — This experiment was designed to show what 

 effect variation in the composition of the mud used would have on 

 the character of the mud-cracks. Three parallel experiments were 

 carried out for this purpose. The fine-textured blue clay of 

 Pleistocene age from the Ottawa Valley was used. A mixture of 

 this clay with 3 quarts of water was divided into three equal parts. 

 To one of these (3a) was added 2 ounces of fine sand. The same 



