86 



diOi<ri University Studies 



3. Stratigrapi'ic Evidence which Precludes the Pressure 

 Theory and Supports the Solution Theory 



Occurrence of Stylolites Only in Soluble Rocks. In- 

 vestigation of the geologic distribution of stylolites reveals 

 indirect evidence that the phenomenon is one of solution. The 

 fact that stylolites occur only in carbonate rocks — varieties 

 of limestones, dolomites, and marbles — suggests solution as a 

 factor, or otherwise they vv^ould not be limited to soluble rock 

 strata (see p. 13). If the pressure theories of Marsh, Giim- 

 bel, Rothpletz, and others explain their origin, why should 

 stylolites not be found in shales, sandstones, etc.? Could not 

 Gumbel's experiment (see p. 27) be applied to rocks other 

 than soluble ones? 



Occurrence of Angular Stylolite-Seams. It is inter- 

 esting to note that in undisturbed strata, such as the southern 

 Indiana limestones, the direction of stylolite penetrations is 

 vertical (with but few exceptions), resulting from the static 

 pressure of the overlying mass; and the direction of the 

 stylolite-seams is usually horizontal, or nearly so, and parallel 

 with the planes of stratification. However, in some instances, 

 stylolites have developed along angular crevices which cut 

 across the stratification (see Fig. 17). A normal fault sur- 

 face, in one case, was stylolitic. In disturbed or metamorphic 

 strata, where lateral pressure has been active, such as in the 

 Muschelkalk of Germany and the Tennessee marble, stylolites 

 run in all directions, the occurrence of vertical seams even 

 being common. Stylolite-sutures which cross one another are 

 observed. Since the pressure theory considers the clay caps 

 of the columns as an original deposit of clay laid down in due 

 order with the rest of the sediments, how can it explain the 

 clay partings of angular to vertical stylolite-seams which cut 

 across the stratification of the rock at various angles? These 

 partings are undoubtedly not original deposits of clay, for 

 they are by no means limited to the stratification planes of 

 the stone (see pp. 44, 54, 67). 



Occurrence of Branching Stylolite-Seams. Commonly 

 there are found two or more parallel stylolite-seams which 

 converge and join into one larger seam, producing what might 

 be called a "branching stylolite-seam" (see Figs. 35 and 36). 

 This major, single seam sometimes continues some distance, 

 and then branches again. The subordinate branches, after 



