566 C. H. GORDON 
transverse sutures was observed by Marsh, but he seems to have 
failed to recognize their negative bearing on the pressure theory. 
Gas theory.—Zelger,’ in 1879, after detailed work on the stylolites 
considers them due to the escape of gases through the soft plastic 
mass and the later filling in of the passageways. 
Erosion theory.—In his description of this structure as it occurs 
in the Bedford limestone of Indiana, Hopkins? reviews the theories 
given therefor and suggests that some may be due to the formation 
of cracks in the drying of limestone mud while others look like a 
rain- or spray-washed surface, though he adds that ‘‘possibly the 
escape of gases, as advocated by Zelger, may have acted in some 
places.” 
Solution theory.—The theory that the stylolitic structure is due 
to unequal solution along suture or fracture planes in calcareous 
rocks after consolidation was first proposed by Fuchs, later accepted 
by Reis,* and more fully established by Wagner.’ Quoting from 
Grabau,° 
if solution takes place on the concave surfaces of both the upper and lower 
faces of the fracture, the result must be the production of a series of tooth-like 
projections from both sides of the fissure, which, owing to the pressure of the 
overlying rock, interpenetrate more and more as room is made by solution. 
In other words the rock opposite the end of each tooth-like projection is dis- 
solved away—the hollows are deepened and the teeth, gliding under pressure, 
penetrate deeper and deeper into the opposite bed while at the same time they 
become longer by the deepening of the hollows which surround and isolate 
them. The residual clay left on solution comes to rest as a cap on the top 
of the stylolite protecting this top from solution. 
The striations on the sides of the stylolite are the result of abrasion 
between the opposing surfaces in the process of compression. As 
the sides of the columns are largely free from pressure there is little 
or no solution there. The presence of a shell or other fossil favors 
the process, as it is less readily soluble than the inclosing rock. 
tZelger, Neues Jahrb. fiir Mineralogie, 1870, p. 833. 
2'T. C. Hopkins, Twenty-first Annual Report of the Indiana Geological and Natural 
History Survey, 1896, pp. 305-8. 
3 T. Fuchs, Ber. d. K. Akad. d. Wiss. Math. nat. Kl. Wien, 1894. 
40. M. Reis, Geognost. Jaresh. d. K. Bayr. Obergamtes Miinchen, Band 14, 1901; 
also Band 15, 1902. 
5 Georg Wagner, op. cit. 6A. W. Grabau, op. cit. 
