T. C. Hopkins — Stylolites. 143 



pointed and sometimes straight. The sides are generally, 

 roughly striated but not slickensided. The line of the seam is 

 nearly always black or very dark-colored. .There is frequently 

 a thin layer of clayey material and rarely a little iron pyrites 

 in the seam. The rock immediately adjoining the seam is 

 frequently blue in color even when the surrounding rock is 

 buff. 



It is the opinion of the writer that the stylolite seams are 

 bedding seams because (1) they correspond with the grain or 

 bedding of the rock, occasionally running on the false bedding 

 but never across the grain ; (2) they are in places traceable 

 with no break or sharp line of division into the common bed- 

 ding planes having no evidence of stylolites ; (3) there is in 

 nearly every instance a layer of carbonaceous material, some- 

 times a mere h'lm, sometimes nearly half an inch thick; (4) 

 they are always of considerable though not unlimited extent ; 



(5) a view from above, shown in a few places on quarry floors, 

 shows water action not unlike the common bedding plane ; 



(6) they frequently occur between the oolitic stone and the 

 underlying Harrodsburg limestone or the overlying Mitchell 

 limestone, beds which are not at all oolitic ; (7) the cross bed- 

 ding always terminates at the stylolite seam ; in no instance 

 was it observed to cross it. 



The explanation of the stylolitic or tooth-like markings along 

 this seam is not so satisfactory as is the evidenee of its being 

 a bedding seam. It is quite probable that they have been 

 caused by different agencies. Some may be mud cracks, some 

 may be due to the action of rain or spray on the exposed sur- 

 face and some may be caused by the escape of gases from the 

 limestone mud. Other agencies may have been active, but 

 the first two mentioned above appear to the writer to be the 

 more probable. 



The following theories proposed by different German writers 

 are many of them suggestive, but do not appear to have met 

 with any favor by the English writers, if indeed they have 

 been consulted. Plieninger* thought that the cracks or crev- 

 ices originating at the surface by the drying mud were the 

 cause, and that the pillar-like or columnar forms could be pro- 

 duced by rain. 



Yon Cotta and Rossmasslerf put them in the same class 

 with the "ice needles" produced on the surface of the soil in 

 winter. 



Fallati and Quenstedt have likened the stylolites to glacial 

 pyramids of ice left on the surface of the glacier, or little 

 pyramids of earth which owe their columnar structure to a 



* Wiirttemberg Naturwiss. Jahreshefte, 1858, vol. xiv, p. 292. 

 f Zirkel. Lehrbuch der Petrographie. 2d ed. , vol. i, p. 585. 



