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Indiana University Studies 



Still more difficult to account for by the pressure theory are 

 the numerous polished and slickensided mineral deposits — 

 usually calcite — on the sides of the columns (see pp. 50 and 

 88). There can be no question but that this mineral matter 

 was deposited there after the rock had become hardened. 

 Further movement of the columns past one another then 

 resulted in the polishing of such deposits. That striations 

 and slickensides were developed while the rock was yet in a 

 soft plastic state appears to be a physical impossibility. They 

 result from the slow slipping of the face of one column along 

 that of the adjacent one, in hardened rock, such as takes 

 place along a fault surface. Striations of stylolites of coarse- 

 grained stone are deeper and coarser than those of finer- 

 grained rock. 



Fig. 33. — Example of an older, curved stylolite pierced by a 

 younger, vertical one. (After Wagner.) 



If stylolites were formed in soft, plastic sediment, as ex- 

 plained by the pressure theory, should not one expect the 

 sides of the alternating columns to be intercemented at the 

 time of the hardening and cementation of the entire rock 

 mass? Such is not the case. 



Direction of Stylolites and Stylolite-Seams. The 

 pressure theory would require that stylolite-seams be de- 

 veloped along bedding or lamination planes where a film of 

 clay has been deposited. Differential compression of the 

 plastic, or semi-plastic, mass would thus produce vertical col- 

 umns at right angles to the bedding planes. However, stylo- 

 lite-seams are developed along inclined bedding planes with 

 the columns not at right angles to them (see p. 54). Such 

 stylolites have been formed subsequent to the folding and 

 tilting of the strata. Folding obviously either occurred after 



