910 



E. M. KINDLE CHARACTERISTICS OF MARINE CLASTICS 



subsiding sediment, and around the tops of these channels small mounds 

 or pits are formed. These are shown in the accompanying photographs, 

 figure 3. Sometimes, instead of either of these, pin-head depressions ap- 

 pear over the surface, but beehive-shaped protuberances with a small 

 opening at the top are the most common. Under ntaural conditions these 

 vertical currents would probably be effective in developing surface feat- 

 ures on the sediments only where deposition was very rapid, as near the 

 delta area of a large river. Where the deposition of mud is going on at 





K", 



Figure 4. — Miul-crack showing tlie upwarped Margins of Polygons 

 This is a characteristic of fresh-water mud-craclj 



the rate of 12 inclies in four days,''' as has been reported by Kellog on 

 parts of the Gulf coast, the features which have been described would be 

 very likely to be developed. Wherever these peculiar and characteristic 

 impressions can be detected on rocks they should furnish evidence of their 

 origin in saline waters as conclusive as that afforded by rain-prints of the 

 subaerial origin of the beds in which they occur. 



Effect of Desiccation on saline and on fresh-v^ater Muds 



The evidence of mud-cracks may in some cases be of value in deciding 

 whether a given terrane is of marine or continental origin. Mnd-cracks 



"Louisiana Gnlf Biological Station, Rnll. P., 1005, p. .S7. 



