142 T. C. Hopkins — Stylolitet 



Art. XYll.— Stylolites ; by T. C. Hopkins. 



Stylolites, " Crow-feet " or " toe-nails" as they have been 

 called by the quarry men, form a very conspicuous feature in 

 the oolitic limestone quarries in Indiana. As they seriously 

 injure a great quantity of otherwise handsome building stone, 

 they have a peculiar interest to the quarry man. The writer, in 

 his recent investigations for an economic report on this lime- 

 stone, was early impressed with the commercial importance and 

 scientific interest of the stylolitic seams. An examination of 

 the accessible literature on the subject failed to reveal a satis- 

 factory explanation.* The only commonly accepted theory in 

 the English literature is that given by Marsh and accepted by 

 both Dana and Geikie in their text-books, i. e. that they are 

 caused by the slipping through vertical pressure of a part 

 capped by a fossil shell against an adjoining part not so capped. 



However applicable this theory may be in other localities, it 

 appears to be untenable in the Indiana oolitic limestone region 

 because (1) a very small percentage, probably less than one per 

 cent, of the stylolites are capped with fossils ; (2) many of those 

 that are capped with shells have a fragile gastropod shell that 

 shows no evidence of distortion or pressure in any way ; (3) 

 in many places where the stylolites are a pronounced feature 

 of the rock, there are shells in abundance a few inches or a few 

 feet above and below the stylolites, but none at or near them ; 

 (4) in many places the stylolites show just the opposite to 

 pressure, occurring along an open bedding seam. 



Other theories which appear to be discarded now are shown 

 in some of the old names, such as lignilites, from their resem- 

 blance to wood, possibly thought to be fossilized wood. Crys- 

 tallites presupposes them to be caused by crystallization, and 

 the term Epsomites that the crystals were Epsom salts. Other 

 names by which they have been known are suture joints and 

 the quarrymen's terms crow-feet and toe-nails. They fre- 

 quently prefix a harsh adjective to these terms. 



Before offering an explanation for their origin a brief descrip- 

 tion is here given, as they no doubt differ in some particulars 

 from stylolites elsewhere. They occur along nearly horizontal 

 seams and appear in the quarry face very much as a suture 

 joint, running nearly horizontal. Projecting both down and 

 up from the general direction of this seam are numerous tooth- 

 like projections which vary in length from a fraction of an 

 inch to five or six inches. The projections are sometimes 



* The views of different German writers mentioned later were not known to the 

 writer until after the formation of his own theory. 



