PREVALENT VIEWS AS TO ORIGIN " 375 



when they contain fossils these remains are seldom flattened by the pressure 

 of the overlying rocks as are those in the surrounding shale. Although many 

 of the concretions which occur in sedimentary rocks were formed while they 

 were in an unconsolidated state and before they were deeply buried, there is 

 no doubt that some were formed after the sediments had been consolidated 

 into rock." 



J. H. Gardner'^ holds that certain concretions which are largely argil- 

 laceous "are contemporaneous with the strata in which they are con- 

 tained." These argillaceous concretions may be flattened clay balls, 

 according to his view. 



E. A. Daly^ has described the concretions in the shale at Kettle Point, 

 Lambton County, Ontario. He states that these concretions occur in well 

 laminated bituminous shales and are pure calcium carbonate. They are 

 spherical, have a radial structure, and have pushed the bedding planes 

 apart. Daly states that the concretions were formed in place within the 

 shale, but that they antedate the period of joint development and final 

 consolidation of the surrounding rock. 



It is not unlikely that concretions have been formed shortly after the 

 first deposition of the sediments, as Daly suggests was the case at Kettle 

 Point, but it is not improbable that the concretions at this locality are 

 syngenetic. Their occurrence along a definite plane, their ra'dial struc- 

 ture and large size, which implies an abundance of material, all favor 

 this view. 



In connection with the last statement, that concretions might be formed 

 in sediments shortly after their first deposition, the possible effect of 

 Liesegang's rhythmic precipitation should be mentioned. S. C. Brad- 

 ford/ in conducting some experimental work on the Liesegang phenom- 

 enon, observed certain concretionary growths in various zones in his agar 

 gel. He pointed out that this might explain the concretionary structure 

 of certain limestones and marls. Such an origin would, of course, be 

 epigenetic, as defined in this paper. There would seem to be little to 

 support the view that a calcareous mud is capable of supporting the move- 

 ment of materials, as is demanded by the Liesegang phenomenon and is 

 so beautifully shown by gels. Experimental studies along these lines and 

 dealing with the materials of rocks are to be desired. 



^ J. H. Gardner : The physical origin of certain concretions. .Tour. Geol.. vol. 16, 

 1908, p. 452. 



8 K. A. Daly : The calcareous concretions of Kettle Point, I.ambton County. Ontario. 

 Jour. Geol., vol. 8, 1900, p. 135. 



" S. C. Bradford : The Liesegang phenomenon and concretionary structure in rocks. 

 Nature, vol. 97, 1916, pp. 80-81. 



XXVII — Bull. Geul. Sue. A.m., Vol. ;51i, 1920 



