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Indiana University Studies 



pp. 135-143), who advocated the view that stylolites were 

 caused by a ''slipping- through vertical pressure of a part 

 capped by a fossil against an adjoining part not so capped" 

 while the rock was still in a plastic state. Marsh's theory is 

 accepted by both Dana and Geikie in their textbooks. 



Marsh made a study of the Niagaran limestones of New 

 York, and published the most exhaustive work that has been 

 done in America on the phenomenon. He presented the 

 geologic conditions essential for stylolitic formation as fol- 

 lows : 



Let us first suppose a quantity of fine carbonate of lime . . . 

 slowly deposited under water, and, while still soft, shells and other or- 

 ganic substances scattered over it, and the whole then covered with a 

 very thin layer of argillaceous mud. If, after this, the deposition of 

 calcareous matter proceeds, gradually forming a second bed, its in- 

 creasing weight will slowly condense the bed below. The shells beneath 

 the clay layer will offer more resistance to vertical pressure than the 

 material around them, and hence the latter will be carried down more 

 rapidly, thus leaving columns projected into the bed above, each pro- 

 tected by its covering, and taking its exact shape from its outline. 



If the shell, instead of lying horizontal, as in the above instances, 

 has an oblique position, curved columns will generally be formed, the 

 curvature being towards the upper edge of the shell and its amount 

 depending upon the degree of elevation. Where the rock is not 

 homogeneous, bent or even broken columns often occur, evidently caused 

 by meeting with impediments, just as a nail is turned from its course 

 when driven against an obstacle. . . . 



The comparatively few stylolites extending from the upper layer of 

 limestone into the lower are evidently formed essentially in the same 

 way as those already described, though under somewhat different cir- 

 cumstances. Where the shape has been determined by a fossil, it will 

 generally be found that this was deposited above the argillaceous layer 

 rather than below it. 



Important conclusions given by Marsh may be summarized 

 as follows: (1) Stylolitic displacement took place in the rock 

 before consolidation was completed. (2) Nearly all of the 

 separate columns have on their summits a fossil shell which 

 has accurately determined their shape. (3) When the col- 

 umns stand at right angles to the stratification, they have 

 been produced by vertical pressure resulting from the weight 

 of the superincumbent strata. The comparatively few stylo- 

 lite-seams which have different positions -are due to lateral 

 pressure. (4) The columns start from the junction of two 

 beds of limestone, separated by a thin seam of argillaceous 



