160 KUMMEL AND WELLER — LIMESTONES OF KITTATINNY VALLEY 



The determination of its age was in fact the basis on which the mag- 

 nesian limestone and the " Potsdam " sandstone were referred to their 

 respective horizons. Foerste's^ later observations confirmed the cor- 

 rectness of the earlier determinations. Rogers observed the basal con- 

 glomerate as early as 1855, at a point where it had been faulted against 

 the crj'stallines. Brief mention of it has occasionally been made in the 

 Geological Reports of the state geologist of New Jersey, but its strati- 

 graphical importance has not previously been recognized. 



Structure 

 folds and faults 



In the Kittatinny valley the rocks lie in several large open folds, the 

 three main limestone areas forming anticlines, and the slate belts between 

 them synclines, with axes trending northeasterl3^ Although in general 

 the structure is thus very simple, in detail it is much more complex. 

 Minor folds occur within the larger ones, more commonly in the over- 

 lying slate than in the limestone. These are frequently closely com- 

 pressed, and vary in radius from a few feet to several rods, or even half 

 a mile. The dips are usually steeper on the southeastern flank of the 

 folds than on the northwestern, so that the axial planes must dip steeply 

 to the northwest. 



Thrust faults occur on the flanks of the folds in a number of cases, 

 cutting out the narrow outcrop of Trenton limestone. The slate belt east 

 of Newton is but half a syncline in its northern part, the westward half 

 having been faulted off. The anticline of Kittatinny limestone along 

 the Paulinskill has been faulted along its crest in such a way as to pre- 

 serve a narrow strip of the Trenton limestone and conglomerate in the 

 midst of the older formation. 



West of Jenny Jump mountain — a huge island of gneiss in the midst 

 of the Paleozoics, forming a detached portion of the highlands within 

 the valley — faulting seems to have been more severe than elsewhere. A 

 fracture along the western side of the mountain brings the Kittatinny 

 and the Trenton limestones, as well as the Hudson River slate, succes- 

 sively against the gneiss. Elsewhere several small areas of the Kittatinny 

 limestone are surrounded by the shale, and apparently rest on it, their 

 position being probably due to thrust faults of considerable extent. At 

 other points, also, the shale has been undoubtedly shoved over on the 

 limestone. The fault planes are rarely exposed, and in many instances 

 the direction and amount of the hade can not be determined. In the few 

 cases observed northwest hades are more common than any other. 



* Foerste, loc. cit. 



