784 PRINCIPLES OF STRATIGRAPHY 



more often they are calcilutytes. The fossils are often broken, but 

 no recrystallization occurs ; the appearance is such as would be 

 expected from the result of gliding of a mass of imperfectly lithi- 

 fied lime mud. The overlying layers have all the characters of 

 normal deposits on the deformed layers, there being thus a struc- 

 tural unconformity, though without a hiatus. (Figs. 168, 169.) 

 These disturbances at Trenton Falls have been variously explained, 

 the general conclusions of geologists being either : (i) that they were 

 truly tectonic — lateral pressure having resulted in the folding of 

 certain strata while others took up the thrust without deformation, 

 or (2) that they were due to squeezing out of certain layers under 

 the weight of the overlying rock masses. Both explanations are 

 unsupported by the detailed characteristics of the folds and their 



Fig. 170. Edgewise conglomerate, Beek- Fig. 171. Section across the 

 mantown limestones. Center county, two interlocking stylolites, 



Pennsylvania. (After Hahn.) shown in Fig. 172, much 



reduced. (After Wagner.) 



relationship to the enclosing layers. The recognition of these layers 

 as gliding surfaces, analogous to the Horgen-Zug occurrences, and 

 comparable to the Oeningen folds, is to the credit of Dr. F. Felix 

 Hahn, at that time curator in Palaeontology in Columbia Univer- 

 sity. (Hahn-7.) 



F. A Cambric or earlier example of such movements seems to 

 be indicated by the folded layers of the Biri limestone of Mjosen, 

 Norway, described by Rothpletz (21). This limestone contains 

 certain layers "which are deformed in a singular manner without 

 the enclosing layers partaking of such deformation. It appears as 

 if, during the tilting, these layers had not enough stability, and 

 collapsed within themselves, so that between the more stable layers 

 there occurred a movement in which the enclosing strata had no 

 part." (Rothpletz-2i : 28.) The characters of these foldings seem 

 in every way analogous to those of the younger formations de- 

 scribed. 



