Stockdale: Stylolites 



85 



show the Harrodsburg Hmestone to contain as much as six 

 to eight times the amount of insoluble constituents as the 

 Salem limestone (compare Table No. 5 with No. 6). 



That the clay partings and the associated stylolites always 

 show a definite chemical and physical relationship is certainly 

 not a coincidence. It is conclusive proof that the clay is a 

 residue from the solution of the limestone. 



Occurrence of Corroded Fossil Fragments in the Clay 

 Residue. The presence of corroded fossil fragments in the 

 clay caps speaks for itself. Altho often only microscopically 

 visible, they are to be found. They are the partially dissolved 

 remains of the original limestone, and make up a consider- 

 able portion of the subordinate calcium carbonate content of 

 the residual clay. 



Subordinate Features of the Clay Caps. Stylolite caps 

 often present a compressed and semi-laminated appearance. 

 Since the circulation of ground waters would be variable, one 

 should not always expect a uniform, even rate of solution to 

 take place. A retardation or pause in the solution would pro- 

 duce a consequent pause in the deposition of the residue and 

 thus give a laminated appearance to the deposit. Altho the 

 line of contact between the clay caps and the ends of the 

 columns is usually sharply defined, a few examples were found 

 which show a slight gradation resulting from a partial solu- 

 tion of the limestone column itself. 



Occasionally, stylolites are found which have what might 

 be termed a ''double cap", where the end of the column is 

 marked by two layers of clay separated by a thin layer of 

 limestone (see Fig. 34). In such a case the solution has been 

 divided between two crevices, and the combined thickness of 

 the clay of the two partings of the one column is equal to 

 that of the single cap of the adjacent column. Analogous to 

 this, a stylolite frequently contains one or more small, sub- 

 ordinate stylolite-seams crossing it at right angles (usually 

 near the end), while the surrounding columns show none. 

 This is nothing more than subordinate solution which has 

 ta'ken place along crevices of this one major -projection and 

 has produced within it minor stylolite-seams (see Fig. 26) . 



