630 



E. M. KIXDLE CANADIAN PLEISTOCENE CONCRETIONS 



their development through lateral deposit of calcium carbonate around 

 the roots. 



The calcareous root concretions appear to have developed only around 

 dead roots. Examination of a great many roots in the beds where these 

 concretions are found has failed to show a single example of the cal- 

 careous tube inclosing a living root. 



By way of illustrating further the influence of roots in causing the 

 lithification of unconsolidated sediments surrounding them, two speci- 

 mens from the Pleistocene shell beds at Saint Augustine, Florida, have 

 been included in the plates (plate 12). In the island east of Saint Au- 



FlGURE 



'Calcareous root Concretions exposed hy loincl Erosion 



gustine extensive beds of unconsolidated sea-shells occur a few feet above 

 the tide, which are occasionally traversed by irregular finger-like masses 

 of consolidated coquina extending down through the unconsolidated shell 

 beds. These irregular masses of cemented shells extending across the 

 bedding are invariably found to inclose a root which has evidently been 

 the active factor in causing the cementation of the shells within the limits 

 of a narrow zone surrounding it (plate 12, figure 1). Sometimes these 

 show a button-like effect, owing to lithification having extended farther 

 into the loose shells in some strata than in others from the root center. 

 The root nucleus of these coquina structures are generally in a very good 

 state of preservation. 



