lOO XEW YORK STATE MUSEUM 



body of granite, but on its opposite border. The first is in the pas- 

 ture on the north side of the road at Barnes's comers, the three 

 comers north of the reentrant. Here the northern end of a strip 

 of garnet gneiss, probably connected with the formation earlier de- 

 scribed (pages 26 and 2><), is cut oft abruptly in the midst of the 

 pink granite (see figure 21). As amphibolite inclusions are absent, 

 the phenomenon concerns only the thin-bedded garnet gneiss. At 

 a point a few yards from the actual termination of the gneiss, the 

 beds strike in a north by east direcuon, which.-is usual for this 

 vicinit}- ; but they then abruptly assume a zigzag strike with general 

 northwest trend, and the whole crumpled formation is cut off by the 

 granite within a distance no greater than the normal thickness of 

 the undisturbed strata. This sudden departure from the usual atti- 

 tude of the gneiss involves crenulations whose complexity' is intense. 

 But when they are seen to conform, as in the previous case, to axes 

 whose pitch is some 2^ degrees toward the northwest, the sedimen- 

 tar}- gneiss takes on the aspect of having had its attenuated edge 

 tucked back upon itself and at the same time compressed by trans- 

 verse crumplings whose axial planes are parallel to the vicinal schis- 

 tosit}'. This phenomenon gives rise to a peculiar effect in the field ; 

 namely, that in adjacent parts of the same outcrop, the most promi- 

 nent structure lines are at right angles to each other. The two are, 

 however, ver}' easily reconciled when it is recalled that one is the 

 general foliation and banding of the gneiss, the other the pitch of 

 local crenulations whose axes and elongation, though necessarily in 

 the plane of the schistosit}-. are normal to its strike. 



In the third case, though the character of the folding is not iden- 

 tical with that just described, it possesses essential points in com- 

 mon; and from the point of view of size is intermediate between 

 the preceding instances and the ver}- much larger Pierrepont sig- 

 moid. This structure is about a mile south of the three cor- 

 ners following the sinuous granite-Grenville contact. It is perhaps 

 a little more difficult to trace in the held than the others on account 

 of the intermittent character of its outcrop. Its main features, how- 

 ever, are shown on the map, where it is indicated as a somewhat^ 

 compressed, tapering, isocHnal sigmoid, quite similar to the struc- 

 ture south of Pierrepont, but possessing an additional quarter tr.m 

 on the top at the northwest side. The features characteristic of its 

 pitch and strike are those common to the other folds described. 

 Plate 20, lower figure, taken about one-eighth of a mile north of the 

 point where this S-fold pltmges imder the surface, looks ver\- nearly 

 in the direction of the pitch, and shows the influence of the lateral 

 compression which tucked up the edge of a zone of injection gneiss. 



