458 JAMES II. GARDNER 



Dr. JMerrill states that this occurronco shows in an interesting way 

 the manner in wliieh certain concretions are formed. 



Another example of the balling tendency of clay particles thickly 

 suspended in current water is shown in the washing of brown iron 

 ores in Alabama.' The clay in the log washers often adheres into 

 balls or concretions and it is necessary to remove these by hand 

 before the ore is sent to the furnaces. There may be serious loss of 

 the iTiner ore particles due to the balls picking them up and carrying 

 them to the waste dump. These mechanical illustrations of the 

 balling tendency of clay are closely similar to those observed to occur 

 under natural conditions in the bed of the Rio Chaco. 



Is it not reasonable to suppose that causes which are now effective 

 in producing concretionary structure have been in operation during 

 past ages of the earth's history ?- 



I W. B. Pliillips, "Iron IMaking in Alabama," Alahaiiia Geological Sui-vey. 



" Since preparing the above article, the writer has been informed by Mr. Frank L. 

 Hess that mud concretions have been observed by him along the Cuyama River and 

 other locaUties in California and by Mr. H. S. Gale along a small tributary to White 

 River, near Meeker, Colorado. No doubt the occurrence is familiar to most geologists. 



In the Umpqua shales (marine Eocene) of Oregon, Mr. Chester W. Washburne 

 reports haA^ing found concretions containing a concentric layer of marine shells; they 

 were in such a position as to indicate that the concretions had been formed b}' a union 

 of particles due to roUing. 



