Stockdale: Stylolites 



83 



brown color, altho the clay of Table No. 4 is black. Ilios 

 (1914, p. 109) points out that 



Carbonaceous matter often serves as a strong coloring agent of 

 raw clays. If present in small amounts it tinges them gray or bluish 

 gray, while larger quantities cause a black coloration. Indeed, so strong 

 may this be that it masks the effect of other coloring agents such as iron. 



li the blue stone contains a greater quantity of carbonaceous 

 matter than the buff, one should naturally expect the same 

 relationship to exist in the residual clays. If the color of 

 the buff stone is secondary, due to an alteration of the iron 

 and carbon content, the question next arises as to whether 

 or not the stylolite-seams originated before or after the color 

 change in the rock took place (sec p. 59). If the stylolites 

 all originated in the blue rock, the writer would believe the 

 stylolite-clays all to have been originally black, \\dth a good 

 percentage of organic matter. The browai clays of today, 

 then, result from a subsequent oxidation and volatilization 

 of the carbon content, the process accompanying the color 

 change of the parent limestone. 



Relation between the Thickness of the Clay Caps 

 AND THE Size and Composition of the Stylolites. In addi- 

 tion to the important relationships between the chemical com- 

 position of the clay caps and the associated limestones, field 

 investigations lead to the following conclusions: 



1. The thickness of the clay caps varies in direct propor- 

 tion to the length of the stylolites. 



2. The thickness of the clay caps varies in inverse pro- 

 portion to the purity of the limestone. 



These two conclusions are logical if the clay partings are 

 the solution residue of the dissolved limestone. In the Salem 

 limestone, the smallest stylolites bear clay caps which are 

 extremely thin, while larger stylolites have clays proportion- 

 ately thicker. Invariably, this relationship is observed. That 

 the thickness of the clay varies in inverse proportion to the 

 purity of the limestone is especially striking in comparing the 

 clays of the stylolites of the impure Harrodsburg limestone 

 with those of the pure Salem limestone (see pp. 80-81). For 

 example, six-inch stylolites of the former have as much as 

 an inch or more of clay, while the same sized columns of the 

 latter bear caps as thin as an eighth of an inch. Analyses 



