A structural analysis of the Wissahickon Schist along the Wissahickon Creek reveals three periods of structural deformation. The F1 folds are predominantly class 2, similar-type folds, whereas the F2 folds are mainly class 1C-type folds (Ramsay, 1967). An S1/S2 cleavage intersection lineation can be traced throughout the main body of the Wissahickon Schist, but S1 is transposed into S2 in the vertically dipping rocks that adjoin the Rosemont Fault Zone. The third deformation is less intense, increases toward the south, and consists of class 1B folds. Podiform, Alpine-type serpentinites have been deformed during D1 and D2 and crop out in the region where S1 and S2 are vertical or slightly overturned. This region may be a root zone for a D2 cover nappe which closes toward the east.

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