98 NEW YORK STATE MUSEUM 



slight variation in the strike of the reversed hmb would be indis- 

 tinguishable from minor undulations of the middle limb. 



Similar but somewhat smaller pitching isoclinal folds are found 

 in various other parts of the cjuadrangle southeast of the amphibo- 

 lite zone of the Pyrites gabbro. These were undoubtedly formed 

 at or about the same time as the Pierrepont fold, and evidently 

 under the same or similar tectonic circumstances, and the easier rec- 

 ognition which their smaller size permits, accentuates the broader 

 principles which, as will be pointed out, governed the formation of 

 all such structures. Three illustrative cases may be noted. 



On traveling southwestward from Little River one soon comes to 

 a rough granite upland of subcircular outline, where the abundance 

 of ledges (plate 18, lower figure), offers ample opportunity for the 

 study of the structural relations of the pink granite and its xenoliths 

 of amphibolite. The southeastern border of this mass is a garnet 

 gneiss injection zone in which the leaf type of intrusion is well 

 displayed. On tracing the periphery of the granite area counter- 

 clockwise, that is, northeastward, one soon comes to a point, at its 

 eastern extremity, where an inner parallel zone of hornblende schist 

 injection gneiss makes its appearance. The amphibolite xenoliths, at 

 first a few scattered streaks and bluntly lenticular masses, increase 

 in abundance till they finally supplant the garnet gneiss entirely. 

 This, meanwhile, has departed from the granite and assumed some 

 unrestricted contortions of its own. The amphibolite zone is typi- 

 cally displayed in plate 19, upper figure. The lenticles are drawn out 

 considerably at their extremities, and numerous black streaks and 

 bands swing round in gently curving lines parallel to their borders. 

 Until one nearly reaches the road, nothing unusual is observed in 

 regard to the character of these curves. Then a pronounced cross- 

 crenulation is developed, which has resulted in the production of in- 

 numerable minute folds (as shown in plate 19, lower figure) whose 

 axial planes are parallel to the general schistosity of the region. 

 Through crumpling, the black and red bands have been very much 

 shortened in the direction of their former course (northwest), but 

 maintain in general their parallelism to the border of the granite 

 upland. About one-fourth of a mile farther on, the next stage in the 

 development of the transverse folding is shown on a larger scale and 

 almost to an extreme degree, in a ledge pictured in plate 20, upper 

 figure. Long streaks of hornblende schist have here been bent 

 back upon themselves transverse to their original course, and 

 compressed to a series of acute zigzag folds, and the trend of 

 the isoclinal limbs is parallel to the schistosity of the environing 



