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Indiana University Studies 



Geologic Occurrence. The conglomerates which have 

 attracted particular attention because of the occurrence of 

 impressed pebbles are: the Nagelfluh (Tertiary) of Germany; 

 the Devonian conglomerate of Scaumenac Bay, Province of 

 Quebec; the Quaco conglomerate, of Quaco, N.B.; and the 

 Bunter conglomerate (Triassic) of England. The occurrence 

 of impressed pebbles, however, is by no means limited to the 

 above-named formations. The most extensive studies of the 

 phenomenon have been made in the Nagelfluh by German in- 

 vestigators. 



Previous Investigations and Theories of Origin. The 

 first to mention impressed pebbles appears to have been A. 

 Escher v. d. Linth, who, in 1833, described those of the Nagel- 

 fluh. Von Dechen, as early as 1849, discussed their presence 

 in the Buntsandstein. The solution theory of their origin was 

 first suggested by Sorby (1863, p. 801). His views may be 

 summarized as follows: The impressions a^e formed, not so 

 much by a mechanical hollowing out, as by chemical solution. 

 Pressure creates heat, which in turn increases the possibility 

 of greater solution. Thus, at the point where two pebbles 

 are pressed against each other, active solution and removal 

 of mineral matter takes place. Continued pressure results in 

 continued solution and a consequent deepening of the depres- 

 sion. Sorby's explanation was confirmed experimentally by 

 Daubree. 



The most exhaustive study of impressed pebbles of the 

 Nagelfluh was made by Rothpletz (1879, 1880). His results 

 show a special connection with the origin of stylolites. He 

 pointed out the occurrence of two limestone pebbles impressed 

 into one another, in which the contact, instead of being 

 marked by a sharp line, showed a minute, jagged interteeth- 

 ing of the two stones (see Figs. 9 and 10) . Since the pebbles 

 were of different colors, the alternating interlocking of the 

 minute teeth was easily discernible. The teeth were covered 

 by a thin coating of iron stain. Rothpletz (1880, pp. 191- 

 192), accepting Sorby 's theory, summarized his explanation 

 as follows: 



While in general the one pebble received, at the point of contact of 

 the other, an impression as a result of the solution of the lime by 

 carbonic acid, yet, certain places withstand this solution better than 

 others so that such places penetrate the opposite sides as pointed pro- 

 jections, thereby forming a sort of teething between the two pebbles. 



