24 



Indiana University Studies 



stylolites to ''earth pyramids" which owe their columnar 

 structure to a small stone or shell protecting the underlying 

 soil, while the surrounding earth is washed away (Hopkins 

 and Siebenthal, 1897, p. 306). This idea of Quenstedt was 

 accepted by Weiss (1868, p. 728), and received its most recent 

 support by Rinne (1905, p. 186). 



In making a study of the Salem limestone of Indiana, Hop- 

 kins (Hopkins and Siebenthal, 1897, pp. 305-308) concluded 

 that in all cases stylolite-seams mark bedding or stratifica- 

 tion planes in the rock. He suggested that quite probably all 

 are not due to the same cause. 



Some look as though they were formed by cracks in the drying of 

 the limestone mud, and others look like a rain or spray washed surface 

 . . . and possibly the escape of gases, as advocated by Zelger, may 

 have acted in some places. 



Gas Theory. The idea that escaping gases may have been 

 a factor in the formation of stylolites was first suggested by 

 Zelger (1870, p. 833). He considered the structures as due 

 to ''the escape of compressed gases through the soft plastic 

 mass, and the later filling in of the passageways" (Hopkins 

 and Siebenthal, 1897, pp. 306-307). 



Zelger's theory had but few followers, one of whom was 

 Potonie, who, in 1910, proposed that the organic substance 

 of the slime, by further decomposition, created gas bubbles. 

 If the gas would collect under a mussel shell in the lime ooze, 

 then the shell would be shoved upward, and the cavity thus 

 formed would be filled in from below, taking the form of a 

 stylolite. 



Bitumen Theory. Another and entirely different hy- 

 pothesis as to the origin of stylolites was suggested by Alberti 

 (1858, p. 292). Having observed the stylolites covered with 

 a dark substance which he regarded as bitumen, he suggested 

 that the columns were formed by drops of petroleum pushing 

 their way upward in the rock which was yet in a soft, viscous 

 state. The hardened petroleum would then serve as asphalt 

 caps. 



2. Two Principal Theories under Controversy 



Two theories of the origin of stylolites have today a di- 

 vided following among geologists. The first, the ''Pressure 

 Theory" — that stylolites are a result of the differential com- 



