Stockdale: Stylolites 



49 



ness of residual limestone clay is a product of the solution of 

 a much greater thickness of parent rock, the propoi'tion de- 

 pending upon the purity of the limestone. 



The differential weathering of limestone is often quite 

 striking. Since the ability of limestone to resist solution is 

 quite variable, even thruout a single stratum, a solution sur- 

 face often presents an undulating and irregular appearance 

 (see Fig. 19). 



EXPLANATION OF STYLOLITIC PHENOMENA UNDER 

 THE SOLUTION THEORY 



Of the above-discussed factors, the writer wishes to empha- 

 size the following two as the most important in the explanation 

 of stylolites : 



1. The effect of pressure upon the solution of solids. 



2. The differential solubility of limestones, and other car- 



bonate rocks. 



Stylolites originate in carbonate rocks — varieties of lime- 

 stones, dolomites, and marbles — along a bedding plane, lamina- 

 tion plane, or crevice, where the circulation of ground waters, 

 charged with carbon dioxide, is most free. Here, then, solu- 

 tion begins. If the ability of the rock to resist solution is 

 slightly variable on one side of the crevice or the other, the 

 carbonic acid would, of course, attack the less resistant parts. 

 If these more soluble portions are distributed first on one side 

 of the crevice, and then on the other, a slightly undulating line 

 would develop, with the undulations becoming more marked 

 after further solution, the outstanding resistant parts of the 

 one side fitting into the dissolved-out portions of the opposite. 

 After the development of this undulating line, pressure (in 

 most cases static pressure, resulting from the weight of 

 the superincumbent strata) plays its role. Most of the 

 weight of the overlying sediment is concentrated along 

 the axis (the top and bottom surfaces) of each of these 

 undulations. This results in an increased amount of solu- 

 tion at the points of increased pressure. The sloping 

 sides of the undulations, which are freer from pressure 

 than the tops and bottoms, are proportionately less attacked 

 by the solvent. Increased solution of the weaker rock 

 opposite the ends of the undulations results in (a) a 



