140 E. M. KINDLE 



In the fresh- water mixture preliminary mud- cracks developed 

 on a dried-surface layer of the thickness of paper two days before 

 the mixture underneath had lost its semi-liquid character. The 

 earlier drying out of this surface layer of paper-like thinness retarded 

 the drying of the lower layers and led to the excessive curling of the 

 polygons as they were cut out by the developing mud-cracks. A 

 lot of closely curled pieces of sediment resembling shavings repre- 



Fig. 5. — Desiccated fresh- water mud. J natural size 



sented the final stage of the mud-crack development in the fresh- 

 water mixture (see Fig. 5). An interesting feature of this experi- 

 ment is the difference in color exhibited by the thin uppermost 

 layer, which had been directly exposed to the air and sun, and the 

 sediment below. The topmost film had a lead-gray color, while the 

 sediment below it showed a creamy- white color in no way resembling 

 the original blue clay. The general character of the mud-cracks 

 shown by this pan corresponds closely to those most commonly 

 met with in nature except in the extreme curling of the polygons. 

 The behavior of the saline mixture was markedly different from 

 that of the fresh-water one. Except for a crack extending round 



