628 



E. M. KINDLE CANADIAN PLEISTOCENE CONCRETIONS 



in others from that of the surrounding clay. The central axis of these 

 structures is marked by a straight tubular canal generally a millimeter 

 or less in diameter, which evidently occupies the position of the small 

 rootlet, which was the determining element in the formation of these 

 incipient concretions. These forms are due to very small rootlets fol- 

 lowing approximately a horizontal direction, while those just described 

 have developed about roots traversing the beds in a vertical direction. 



Figure 2. — SKetch shoicinfj tico Levels of clay Pits southwest of BUlimjs Bridge 



Each level carries a distinct type of concretion. The pencil-shaped root concretions 

 (plate 11, figures 11, 12) and the marlekor (plate 10, figures 2-5) are confined to the 

 lower level, and the non-indurated concretions (plate 13, figures 13, 14) to the upper level. 



Although without differentiating hardness, they show a beautifully sym- 

 metrical structure, which is often apparent to the eye only through the 

 concentric layers of lemon and pale brown which define the several zones 

 of slightly different composition developed by concretionary growth. 

 These concretions differ from the root concretions already described and 

 another type to be mentioned later in their bulging barrel-shaped sides 

 and torpedo-shaped ends. They lack the considerable length, often 

 amounting to 1 or more feet, shown by the root concretions, and have 



