364 E. B. MATHEWS AND W. J. MILLER, — UOCKEYSVILLE MARBLE 



is, moreover, a torsional feature in these faults which is of especial inter- 

 est. The thrust at the northern end of the fault is slightly to the east- 

 ward, as in the vicinity southwest of Hess, where the Setters quartzite 

 may be found above the Wissahickon and limestone if the latter is 

 present. Along the central and southern portions of the fault line, how- 

 ever, the thrust is westward. The relationships may be most thoroughly 

 studied in the valley of the Gunpowder at Warren, where it is quite 

 clearly shown that we have a somewhat complex anticline plunging to 

 the northward with a compressed fold in a line passing through the 

 town of Warren. 



The anticlinal character of the folding is evident (figure 2) east of 

 Warren near the mouth of Royston branch, where the Gunpowder flows 

 in a gorge cut through the Setters quartzite and " pseudo Wissahickon " 

 (the garnetiferous upper portion of the quartzite formation) and Cockeys- 

 ville marble to the contact between the latter and the underlying Wissa- 

 hickon, which it follows southward to Dulany valley. The strikes and 

 dips as shown in the valley of Royston branch indicate at this point a 

 northward plunging anticline, the west limb of which. is replaced by the 

 fault under discussion. The Wissahickon schists may be traced con- 

 tinuously around the anticline to the Gunpowder river immediately 

 west of Warren bridge, where they are found striking to the south and 

 dipping to the west or east, as the case may be. Near the quartzite on 

 the south side of the Gunpowder the strike is southwesterly, and the dip 

 is toward the east as a result, apparently of the overriding of the quartz- 

 ite at this point. In the stream bottom beside the road leading from 

 Warren to Cockeysville on the line of the fault is a recemented breccia, 

 which indicates a portion, at least, of the fault zone. 



The structural features of this locality indicate that the forces at work 

 were northwest and southeast, and that the thrust, which here is slight 

 as compared with that farther south, carried the Baltimore gneiss, quartz- 

 ite, and marble across the Wissahickon formation. 



The structural features along the southward continuation of this fault 

 are much obscured by the intrusion of a granite mass which forms the 

 eastern boundary of the Wissahickon and probably occupies the eastern 

 side of the fault, where one would naturally expect the Baltimore gneiss 

 if there had been no granitic intrusion. 



The southern fault, which extends from near Lutherville to south of 

 Mount Washington, is similar in character to that already described 

 about Warren, but much more pronounced. 



The accompanying sketch map* (figure 2) of the valley of Jones falls 



*The relative position of the detailed maps may be indicated approximately by placing the 

 southwest corner of the neat line of figure 1 over the northeast corner of figure 2. Both figures 

 oriented north and south, 



